Clearly, at the moment, FreeUndelete is top of the pile for me but I do, of course, have a number of other free apps I can recommend - though, unlike FreeUndelete, the authors of these programs would very much like you to make a contribution to the upkeep of the programs.
Anti-nasties
Nothing unexpected here:
Anti-trojan:
AdAware Free (I bought the Pro version, cos I was so impressed)
SpyBot Search & Destroy
HiJack This (not a tool for the novice but VERY useful)
Anti-virus:
AVG Free
Zip-file uncompressor:
I long ago paid for WinZip and use the latest version happily still. However, the 7zip freebie is excellent. If Rar, rather than Zips are you thing, then WinRar is good too.
HTML-creation:
NVU
Web browser:
Mozilla FireFox, of course
Email:
Mozilla Thunderbird, naturally
FTP uploads and downloads:
FileZilla FTP (truly wonderful)
Hi-def video player (and very much more - truly amazing what it can do):
VLC
Analysis of video Codecs installed on a PC:
Sherlock (the Codec Detective)
Identifying what Codec a video file has been encoded with:
AVI Codec
Any more for any more?