7-Zip

There are a good number of free file archivers for packing/unpacking, however a fair few you are only getting a freeware version of the full product (sometimes one that occasionally nags you to get the full version). However 7-Zip is open source and has all the features you could want.It supports:

• Packing / unpacking: 7z, ZIP, GZIP, BZIP2 and TAR
• Unpacking only: ARJ, CAB, CHM, CPIO, DEB, DMG, HFS, ISO, LZH, LZMA, MSI, NSIS, RAR, RPM, UDF, WIM, XAR and Z.

It is incredibly lightweight and fast at what it does, while still boasting some of the best compression rates.