DaFont: an excellent free font resource
Heads up! This post was written in 2007, so it may contain information that is no longer accurate. I keep posts like this around for historical purposes and to prevent link rot, so please keep this in mind as you're reading.
I came across an excellent website for free fonts online. No annoying pop-ups, minimal banner ads, and the best feature of all — custom previews for all their fonts.
Check 'em out at dafont.com.