Be sure to review this post here on AT:
Freeware
Be sure to go down the list of things in your Device Manager to find & install any driver updates, so you have latest divers.
Here are some free things I find useful, your mileage may vary:
AOL Kaspersky antivirus
Firefox web browser and appropriate add-ons.
FireFTP for Firefox so you can ftp
Thunderbird e-mail client
7-zip file unzipper/zipper
uTorrent bit torrent client
Spybot Search & Destroy cleaner
Lavasoft Ad-Aware cleaner
The Runners Log by Wade Humeniuk
Rainlendar2 calendar, to-do list, task list & reminder
vidalia-tor-privoxy proxy bundle
Picasa2 photo utliity to post to web
Foxit PDF reader (don't install fat fat Adobe Acrobat reader!)
OpenOffice suite (like Word, Excel, Powerpoint)
Google Earth
Free Download Manager
VideoLAN VLC Media Player (don't remove WMP, just ignore WMP because VLC works better. It's unlikely you'll need any supplemental codecs for VLC. It pretty much comes native with everything you'll need in codecs)
DVD Flick, to convert video file formats into DVD format
CCleaner clean - up tool. Run it frequently
Arachnophilia HTML authoring app
Notepad2 HTML authoring app, not as good as Arachnophilia but simpler to use
Adobe Flash player
Adobe (Macromedia) Shockwave player
Sun JAVA
Microsoft Virtual PC 2007
Belarc Advisor
Contig defragmenter from Microsoft and Power Defragmenter gui (not from Microsoft) to run Contig
DupDetector tool to discover duplicate files on your computer
Depending on your hard drive brand, maybe Maxtor Maxblast or Western Digital Data Lifeguard Tools, or whatever other free backup app your hard drive brand may offer
MozBackup to back up Thunderbird e-mail and settings, and Firefox settings
EasyCleaner registry cleaner
cpuz tool
Ritemark Memory Analyzer tool from CPU RightMark
OCCT! stress test
Prime95 stress test
SP2004, same as Prime95 but with helpful gui
TCPOptimizer
TweakUI from Microsoft
SIW (System Information for Windows), is same general idea as what used to be Everest Home Edition
nLite slipstream tool
Undelete Plus to recover deleted files
Cute partition manager, to adjust hdd partitions. (I use Partition Magic instead, not free)
Hosts file, update your system with the newest rev every 2 weeks,
from here
Country Codes Lookup Tool by Saber Naeemi
Just for fun
edit: deleted "Mathematica for Students" from the list, which I had included by mistake, as pointed out by
Narmer in his post below. Thank you
Narmer.