BMP - Windows Paint simple to use format, good quality but large files.
CLP - Clip Art for including in drawings, documents etc.
CHT, CH3, PR4 - Harvard Graphics presentation graphics.
JPEG, JPG or JPE - a very common format frequently used for photographs. Allows for compression to save on file size but high compression results in loss of quality.
GIFF - commonly used for Internet graphics, eg on websites. Reasonable quality, compression. Originally created by Compuserve).
PCX - an oldish format, good for clip art
PCD - format used on commercially produced Photo CD's
PSD - Adobe Photoshop file. High quality and layers can be edited, large files.
RAW - raw graphics file produced by digital camera's
TGA or VGA - Targa (don't know anything about it!)
WPG - Word Perfect Graphic, used by the Word Perfect Corporation.