Hmmm...
Unit Converter cool little utility that lets you convert from one measurement system to another (extensible with your own formulas)
The foundstone free tools (mostly security and network stuff)
Seagull Free FTP client not as slick as some others, but does a great job getting FTP data when the connection is bad (just keeps retrying in mid-capture)
Popfile - a great spam filter (baysean filter, simply
marks categories in a header field, your email client then needs to do "whatever")
Privoxy a http "proxy" that can remove ads, "web-bugs", whatever.
I guess that's all I can think of that haven't already been mentioned...