Terragen is awesome!!! I used to sit for hours playing around with it. You can make some very cool scenic pictures with it too. Very fun!! I'd recommend it to anyone. Renderosity has a great gallery of work done with it.
Wings3d is pretty cool if your into 3d. Back when I was in college one of my professors modeled a head with it in 5 min. I downloaded it and played around a bit. That was 6 years ago though, and 3d technology has came far since then. It's a pretty solid program though.
AVG and Adaware I'd recommend to anyone who can't afford other anti-virus. Hijackthis is good if you know how to read the reports.
I'm sure there's more, but those are some good ones. I'm going to go peek around here now
. I loooove free stuff!! Thanks for the list!