Firefox
Thunderbird
OpenOffice
Codec Pack + Media Player Classic
Winamp
Ad-Aware / Spybot S&D
anti-virus (AVG)
burning software (CDBurnerXP Pro)
SmartFTP
ZipGenius
Metapad
That's my 10 (well, 11 or 12)... everything listed is free!
If you have some money, Trillian Pro is well worth the $25.