Each hieroglyph is given an alphanumeric code so it can be written using the letters and numbers of western society. Each code is referred to as the symbol's Gardiner Code. For example, the first symbol in the countdown timer, folded cloth, has the code "S29".
These hieroglyphs, known as "folded cloth", "curl", "fire drill", "vulture" and "stick", correspond to symbols S29, Z7, U29, G1, Z6 from Gardiner's Sign List. Raymond O. Faulkner's A Concise Dictionary of Middle Egyptian, translates a virtually identical sequence (below), substituting only U29 for U28, as "die".
The first line corresponds to the symbols A26 S29 M17 and N35 (Man With Out-stretched Arm, Folded Cloth, Blooming Reed, Water). The second line corresponds to symbols A24 W24 and Aa27 (Man With Weapon, Pot, Unknown). Unlike most other hieroglyphs on the island, these appear to read right to left.
N35:M17*S29-A26 translates as "summon".
Aa27-W24:D36 (Unknown, Pot, Arm) translates as "protection", and determinately symbol A24 (Man With Weapon) may function, in this case, the same way as symbol D36 (Arm). Roughly translated, then, they appear to read "to summon protection...".  Unlike the image from the Season 4 DVD extra, the actual door appears to have the aforementioned hieroglyphs plus V18 (amulet), which translates as "protection", reinforcing the interpretation of the second line.
The frozen wheel used to move the Island is within a rock chamber with a rock column in the middle that is inscribed with hieroglyphs. Some of these hieroglyphs are very similar to the hieroglyphs on The Temple. Just below the lamp, can be seen a set of hieroglyphs that correspond directly with one set on The Temple:
Another view of the column.
These translate as "travel". Near the bottom of the column is another set of hieroglyphs that is not entirely visible from any one angle, but a composite of images shows that it is
The boarding pass featured on ajirairways.com  has hieroglyphs in semi-transparency in the corners and along the top and bottom of the sample pass. Visible are the same five hieroglyphs from the countdown timer: S29, Z7, U29, G1, and Z6, which producer Damon Lindelof translated to mean "underworld".
Hieroglyphs can be seen on the temple wall where Jin finds Montand's rotting arm. ("This Place Is Death") Specifically, the hieroglyphs surround the declivity in the wall. Two of the sets of hieroglyphs on the Temple
Paul, a member of the DHARMA Initiative who died in the episode LaFleur, wore a necklace with an ankh hieroglyph pendant. The ankh was often carried as an amulet by ancient Egyptians. In modern times, the ankh has been used as a symbol since the 1960s, often in association with cultural movements.  Paul's wife, Amy, took his ankh from him after his death. She is seen breathing into the pendant which is considered to be an offering of "The Breath of Life". The breath you will need in the afterlife. Later, Amy's subsequent husband, Horace, found the memento among Amy's things and became upset. ("LaFleur") This symbol, which means “life”, was often used to show Pharoahs as having been conferred with life after death. As such, the symbol is often associated with immortality. 
For an "in-progress" transcription of the hieroglyphs seen in the Cerberus chamber, see The Temple hieroglyphs.
Within the declivity in the Temple wall, underground, Ben found a chamber with many hieroglyphs and other symbols of Egyptian religion (including an engraving of the Monster facing the Ancient Egyptian god Anubis). The majority of these hieroglyphs were written in a cursive form, and so deviate from their formal counterparts to varying degrees. Cursive hieroglyphs were most often used from religious writings in Ancient Egypt. ("Dead Is Dead")
A lesson on Ancient Egypt and hieroglyphs was taught in the DHARMA classroom. ("Some Like It Hoth") Below is a summary of the contents of the blackboard, which includes both hieroglyphs and descriptions of the Egyptian language. The first line of hieroglyphs is a phrase that means "Egyptian (language)". The second line translates as "Writing of the words of God". The third line means "Egypt".
2600BC to 2000BC Tripling ideograms, phonograms, and determinatives
Within The Tunnels, a series of underground tunnels controlled by The Others, there are numerous pillars identical to those found in the Cerberus chamber. The sequences of hieroglyphs on those pillars are identical, and so can be found on the page where the hierglyphs are currently being transcribed: The Temple hieroglyphs
Along with Greek writing, numerous hieroglyphs can be seen on Jacob's tapestry. ("The Incident, Part 1") For example, near the right tip of the wings extending from the Eye of Horus can be seen the sequence D36-V30:Z2 (see below), which would translate as "appoint lords" or "lords give/grant". 
The three Egyptian seasons appear to be written near the bottom of the tapestry (series shown below). The center and right hieroglyphs mean "winter"  and "summer"  respectively. The left hieroglyphs are likely a variant of the third egyptian season "inundation", which is usually written M8:Aa1*X1, but is here written Aa1-M8:X1. 
Most of the hieroglyphs in The Temple are not yet translated, but above the pool can be seen a series of hieroglyphs that are a conjunction of words (in a sense). The series, seen below, likely translates as "The Primaeval Waters of Nun". Nun, as a deity, represents the water from which all creation formed.
Translating hieroglyphs is difficult and inaccurate. First, hieroglyphs may be written left-to-right or right-to-left, although key symbols, such as humans and animals, were supposed to be drawn to face towards the beginning of the sentence. It can also be challenging to identify where one word stops and another begins. Correctly identifying each symbol can be a challenge, as some hieroglyphs are drawn less clearly than others, and some hieroglyphs look very similar. In religious writings, cursive forms of hieroglyphs, which can vary from their originals significantly, were also used. To further complicate translation, each symbol can mean something on its own (ideogram), represent a sound (phonetic), or give you a clue about the word written before it (determinative).
For example, S29 (folded cloth) represents the idea of 'health' (ideogram). However, S29 also represents the sound 's' (phonetic). Since most of the words written in hieroglyphs are missing many or all of their vowels, it can be hard to know what a word spelled phonetically means. It would be like trying to figure out what the word "crs" means if our writing didn't include vowels. It could mean "Cures", "Curse", or "Cares", for example. In hieroglyphic writing, then, a symbol will be placed at the end of a phonetically spelled word in order to give the reader a clue as to which possible meaning is intended (determinative). For example, if you wrote the word "crs" and put a heart at the end, you might assume the word meant "cares", whereas if a symbol of evil (like the hieroglyph Z6-Enemy) was placed at the end of the word "crs", you might assume the intended word was "curse".
Series of hieroglyphs
The following table summarizes the sets of hieroglyphs seen so far, relevant information associated with them, and citable translations.
* links to uncropped image
"Travel north" or "travel downstream" or "flow (of water)" or "North" 
The following table summarizes the phonetics and meanings associated with the hieroglyphs seen so far, as well as some related hieroglyphs. Note that many of the symbols seen under The Temple Wall were alchemic, not hieroglyphic.
Man pointing hand at mouth
"Eat" or "drink" or "speak" or "think" or "feel" or "tell" or "refrain from speech" or "advise/counsel" or "love" 
In the Lost Untangled for "Follow the Leader", hieroglyphs are visible on the pillars within the Tunnels. While the hieroglyphs are real hieroglyphs, they do not match the actual hieroglyphs as shown in the episode.
Lost University offers a course on hieroglyphs called Ancient writings on the wall.
An advertisement for Mysteries of the Universe, a short series of videos about the DHARMA Initiative, includes an image of a film reel, along the edge of which can be seen a row of hieroglyphs. The series, seen below, represents the phrase "nm sSmw", which loosely translates as "Who is the leader?":
The season 6 promotional poster containing hieroglyphs.
In a season six promotional poster, hieroglyphs can be seen drawn within the phrase "THE FINAL SEASON". This series of hieroglyphs is the same as seen in the Mysteries of the Universe advertisement, and so translates as "Who is the leader?"
Professor Erik Wells' image, with hieroglyphs in the background.
Hieroglyphs on U.S release of Season 5 Blu-ray set.
When the student enrollment countdown timer at the Lost University website reached zero, a series of hieroglyphs were shown. The left portion of the glyphs, shown on the black background, translates as "ordain, order, predestine, assign, settle, or decide".  The right portion of the glyphs, shown on the red background, likely translates as "he who is summoned, or reckoner".  Together, then, the series could be translated: "The summoned one ordains it."
The Lost University image of Professor Erik Wells, who is one of the professors for the course about hieroglyphs, is standing in front of a whiteboard with hieroglyphs written on it. These hieroglyphs are G17-Q3*X1:N1, as seen below. G17 can translate as "with, by means of, from, out of, as, namely, when, as, though, or together with".  Q3*X1:N1 translates as "sky or heaven".  Together, then, the series would translate as "from the sky", or "out of heaven."
The same series of hieroglyphs as had been seen on the countdown timer on the Lost University website are shown (obscured) on the Season 5 Blu-ray cover.
Duncan Crawford (a.k.a. Skulboy [sic]), is an artist who sculpted many of the hieroglyphic pieces shown on LOST, including the pillar in the Frozen wheel chamber and the mural in the The Cerberus chamber. On each of these sculptures, he carved a hieroglyph-like skull as a signature.