Photos and images:
JPG - Pictures stored in digital cameras and on the Web (Joint Photographic Experts Group)
PNG - Portable Network Graphics
GIF - Graphics Interchange Format
BMP - Windows and OS/2 bitmap image
TIFF - Tagged Image File Format
ICO - Windows Icon
ANI - Windows Animated Cursor
CR2 - Canon RAW image
SR2 - Sony RAW image
NEF - Nikon RAW image
DCR - Kodak RAW image
PEF - Pentax RAW image
DNG - Adobe Digital Negative
SVG - Scalable Vector Graphics
PSD - Adobe Photoshop Image
RAS - Sun raster image
PSP - Paint Shop Pro image
Thumbcache - Windows thumbnail cache
IFF - Amiga images and other media
ART - AOL Art images
WMF - Windows MetaFile
EMF - Enhanced MetaFile
WMZ, EMZ - Compressed MetaFiles
DICOM - Medical imaging format
WEBP - WebP images
PCX - ZSoft PCX images
CDR - CorelDraw images
INDD - Adobe InDesign documents
CP - Adobe Captivate documents
Documents:
DOC - Microsoft Word document (2003 and below)
DOCX - Microsoft Word document (2007 and above)
XLS - Microsoft Excel spreadsheet (2003 and below)
XLSX - Microsoft Excel spreadsheet (2007 and above)
PPT - Microsoft PowerPoint presentation (2003 and below)
PPTX - Microsoft PowerPoint presentation (2007 and above)
VSD - Microsoft Visio document
PDF - Portable Document Format
XML - eXtensible Markup Language
HTML - HyperText Markup Language
RTF - Rich Text Format
WPD - WordPerfect document
WPS - Microsoft Works document
PUB - Microsoft Publisher document
XPS - XML Paper Specification
WRI - Old Windows Write document
ODT, ODS, ODP, ODG - OpenDocument formats
Audio and video:
MP3 - Audio format widely used in digital media players (MPEG layer 3)
WMA - Windows Media Audio
AVI - Audio Video Interleave
WAV - Wave audio
MID -Musical Instrument Digital Interface
FLV - Adobe Flash Video
WMV - Windows Media Video
MOV - QuickTime video
M4A - MPEG-4 audio
M4V, MP4 - MPEG-4 video
3GP - Third Generation Partnership video
F4V - Adobe Flash video based on MPEG-4 Part 12
RM - RealMedia video
RMVB - RealMedia video (variable bitrate)
MKV - Matroska video
MPEG - Motion Picture Experts Group
AU - Sun Microsystems audio
MTS, M2TS - MPEG2 Transport Stream
R3D - RED Video Camera video
APE - Monkey's Audio file
OFR - OptimFROG lossless audio
PPM, PGM, PBM - Netpbm images
WEBM - WebM videos
Compressed archives:
ZIP - Widely used compressed format developed by PKWARE
RAR - Roshal ARchive, used by WinRAR
7Z - Compressed format used by 7-Zip
GZ - Compressed format used by gzip
SIT - Compressed format used by StuffIt for Mac
ACE - WinAce archive
CAB - Microsoft Cabinet archive
SZDD - Compressed files created by COMPRESS.EXE from MS-DOS
Miscellaneous:
ISO - Images of optical media, such as CDs and DVDs
EXE - Windows or MS-DOS executable file
DLL - Windows or MS-DOS dynamic-link library
MDB - Microsoft Access database (2003 and below)
ACCDB - Microsoft Access database (2007 and above)
PST - Microsoft Outlook Personal Folders file
DBX - Microsoft Outlook Express data file
XAC - GnuCash data file
KMY - KMyMoney data file
DWG - AutoCAD drawing
DXF - Drawing Interchange Format
CHM - Microsoft Compiled HTML Help file
TTF, TTC - TrueType font
CLASS - Java class file
KMZ - Google Earth location data