If you aren't into using trials that will bug you to register, then 7-Zip is a freeware program that is actually nicer than WinZip in some respects.
Supports lots of formats: 7z, ZIP, CAB, RAR, ARJ, GZIP, BZIP2, Z, TAR, CPIO, RPM and DEB
7-Zip.org
I forgot about 7-Zip until I saw this thread, so I'm about to switch back again
