some free software i find extremely useful

here is a list of software i find to be amazingly useful. many of the programs on this list are either open-source alternatives to otherwise expensive programs or more effective alternatives to the programs that come packaged with operating systems.

general maintenance:

• CCleaner: this is a powerful computer cleaning program. it handles uninstalling, mass deleting, startup programs, and more. it also has the ability to actually delete information off your hard drive(not just write over it), just like the spies do.
  
• Defraggler: if you use any of the vista kernel OS, then you know how annoying the built in defragmenter is. defraggler gives you a more "XP-esque" experience that actually allows you to see what it's doing among other neat features
  
• Gparted: this program it the most reliable partition manager out there. it is a live disc, so it operates outside of the operating system, dodging any pesky permission issues. a must-have when dual-booting your computer.

media/office:

• VLC media player: this is a bare-bones media player with the capability to play every imaginable public codec imaginable. small and fast, it outperforms any i have seen to date.
  
• WinAmp: winamp is a powerful and versatile media player that runs faster than most. it can even put music on your ipod.
  
• Open office: open soure (free) alternative to the microsoft office suite.

i'll put more up as people suggest/ i think or them.

You forgot a few...
-Irfanview, to replace the crappy vista/win7 image viewer
-K-lite codec pack + Media Player Classic, great alternative to VLC with codecs which can be used by ANY program. A must for any video editor!
-CamStudio, open source desktop recorder. Uses little resources and also works with external codecs
-µtorrent, light weight torrenting client.
-Firefox and/or Chrome, the two best browsers for everyday usage.
-X-mouse control, allows custom (keyboard) binds to your mouse complete with binds for only one program and multiple bind layers! Ideal if games have trouble accepting mouse4, mouse5 or tilt wheel (like Source games).