[7zip][1]

  - It handles all major formats and works *incredibly* fast.  
  - And is free. 
  - And has great windows integration via context menus. 
  - Small footprint 
  - Lets you explore archives without extracting them.
  - And you can use it in the shell.
  - [Supports multi-volume archives.][2]
  - *Mostly* licensed under LGPL


  [1]: http://www.7-zip.org/
  [2]: http://beta.stackoverflow.com/questions/5383?sort=votes#8283