brain dump of some useful utilities, in no particular order:
1) F.Lux - makes your screen more "orangy" as the day progresses. Supposedly makes it easier to go to bed because you haven't been staring at an ultra bright, blu-ish tented display until midnight and then can't get to sleep.
http://stereopsis.com/flux/2) Fences (thanks n3rdl1f3) - allows you to build "fences" on your desktop and basically categorize desktop icons into boxes that you can arrange anywhere on your desktop. The paid version adds features but the free works just fine.
http://www.stardock.com/products/fences/3) CCleaner - cleans up after programs that love to keep history and cache of everything you do, cleans up (but doesn't fix) registry crap, helps nuke programs that won't die, just all-around nifty utility. It natively supports all major browsers, goes after the hard to find adobe flash cache files, java cache files, etc, etc. It's updated regularly to add new apps and to keep cleaning up after apps already out.
http://www.piriform.com/ccleaner4) Disk Defrag - Does a better job than the built-in one that comes with Win7 and it's free
http://www.auslogics.com/en/software/disk-defrag/5) Recuva - free file recovery utility. I'm sure there are better ones out there, but most charge a lot of money and this one works decently well and is free.
http://www.piriform.com/recuva6) Filezilla - free very good ftp client and server. I use both all the time to ftp files to and fro. The server is especially nice because it fully supports secure ftp which allows you to transfer files without anyone snooping.
http://filezilla-project.org/7) XBMC - if you don't have a box running xbmc in your living room, you are missing out. GREAT tool for streaming content from various sources on your home network and putting it all together in a nice 10foot interface. Great community and it continues to be updated. Also, it will play EVERYTHING you have. i don't think there is a codec that it can't play. Can't say the same for PS3 or Xbox360, etc.
http://xbmc.org/8 ) Sysinternals - long time ago there was a company that made SysInternals. MS bought them and we thought it was the end of some REALLY useful utilities. Well, the dude that made them, continues to make them, and they continue to be AWESOME. Dig into what's running in memory, what is using up your bandwidth, what registry entries a program is hitting when it's loading or running, etc, etc. Tons of invaluable utilities. I personally love procmon and procexp. Rammap will scare you with what all is still visible in memory even after you've closed an app.
http://technet.microsoft.com/en-us/sysinternals/bb5450219) TheRenamer (thanks cypher) - great tool to make your tv show collection (that you legitimately ripped from your own store-bought dvds) orderly with properly formatted filenames and folder structure.
http://www.therenamer.com/10) 7zip (thanks cypher) - i didn't know about this until about a year ago. Great little utility for extracting compressed files (and creating compressed files) quickly without any big interface, crap running in your systray, or annoying nags to buy it. Just right-click on an exe, zip, rar, etc, choose 7zip and extract.
http://www.7-zip.org/