Ashampoo WinOptimizer 6: Similar to System Mechanic but won't jack up your sh*t. And it's FREE. Go get it! *Also try CCleaner if you're too slow and couldn't get this for free. Just as good.
Combined Community Codec Pack: Can't watch those .mkv .avi .mpeg .asf .mp4, etc... files of pr0n you downloaded? You need this. It even comes of Windows Media Player Classic.
ImgBurn: You never know when you want to "backup" your Madden 11 onto a dual layer DVD or "backup" that Bluray movie/game.
NOD32 AV: Solid AV program. I've used almost all the antivirus programs out there including Norton AV/security suite, McAfee, AVG, Kaspersky, Avast, and Symantec, and NOD32 blows all these out of the water.
Why? NOD32 doesn't hog system resources like Symantec or Norton (POS had a few memory leaks which started to drain my memory of 600megs) or label your special files as viral (check Kaspersky, McAfee...). It's quite user friendly (by user friendly I mean noob friendly). Constant definition updates though nothing can protect your from zero day baddies.
Peerblock: Do you torrent? Might want to look into this. It won't completely protect you from prying eyes but it'll at least stop the boogey man from scaring away your PC.
Skype: Call your friends. Live chat with them. Send free text messages. Seriously, why are you even paying for texting?
Utorrent: Clean. Simple. Does what it's suppose to do which is to torrent. If you want a million addons and miscellaneous wares, get Vuze, Azureus 8.0.
Decaf: If you don't know what this is, you don't need it.
Truecrypt: If you don't know what this is, you don't need it.
For Firefox users, Foxyproxy is very useful.