Here is a link to another list of common Internet File Formats.

.Z	UNIX COMPRESS (ONE file compressed)

.GZ	GZIP (GNU ZIP, freeware/PD, _NOT_ compatible with .ZIP)

.ZIP	PKZIP or INFOZIP (PKZIP is the originator of the format, and
	INFOZIP is a PD implementation with source available for
	producing the program on various platforms).

.LZH	A fairly popular compressed file format.  From Japan.

.ARJ	Yet another fairly popular compressed file format.

.ARC	An older compressed file standard.  ZIP is much better, but
	you'll probably still encounter these files.

.TAR	Tape ARchive format.  A UNIX backup, any file may include
	compression, but TAR doesn't imply "compressed".  I've yet to
	find a good TAR implementation for the PC.  If you do, drop me
	a line.

.GIF	Graphics file.  Max 256 colours (8 bit).  This is a common file
	type, originally developed by CompuServe.  Unfortunatley, Unisys
	owns the patent to the compression algorythm used in the format,
	and has been demanding royalties for its use, so expect the use
	of this to start dropping off.

.JPG
.JPEG	Graphics file.  Max 16M colours (24 bit).  Popular in picture
	groups, because it compresses very well ("lossy compression"),
	and supports 24 bit colour.  Also used in many graphically-rich
	web pages.  They tend to be smaller than a GIF file, and better
	quality (more colours), but the decompression time (to make the
	file viewable) takes much longer than for GIF.

.MPG
.MPE
.MPEG	Compressed animated video file.  Requires a viewer application, or
	a browser which properly supports MPEG.

.XBM
.XPM	Bitmap (black and white), and pixelmap (colour) files respectively.
	They're supposed to be supported by most web browsers, much like a
	GIF file, but one doesn't come across them too frequently.

.HTM
.HTML	WWW file -- view with your WWW viewer.  .HTML is the official
	form, but .HTM is the common abbreviation for PC systems which
	limit the extension to 3 characters.

.AU	Audio file (gernerally speaking, the UNIX equivalent of .WAV).
	The Windows sound recorder won't touch this.  NetCruiser v1.60
	supports playing these (either as file attachments in Mail, or
	from WWW).

.UUE	Often used to refer to a UUEncoded file.  UUEncoding is a way of
	converting a binary (8 bits per character) file into a text
	(6 bits per character) file.  This involves taking two characters
	from the binary file (16 bits) and making three characters in the
	uuencoded output file (18 bits, but they REALLY TAKE 24 bits).
	This may seem like a waste of space (and it is), but it makes files
	compatible with the old network standards in place on the Internet.

I found a FAQ on graphic file types. Here it is: Graphics File Formats FAQ