I will attest to the awesomeness that is Sam and Max... I haven't gotten around to playing episode 4 all the way through but it has been funny. Anyone still have the old Sam and Max? Man, those were good times...

I'm going to throw in my vote for best free game:

Desktop Tower Defense

This is a flash based game, but it's addictive as hell. I must have played it for a week straight after work. The object is to block and shoot down "creeps." You do this by building towers and mazes... I'm not going to spoil it by posting some strategy, just give it a try and find a technique that you like... For the record, I've been able to beat normal, but I have only been able to get to level ~80 on Fun -> 10k gold.

Good luck!

Interesting little article for any of you cheap wads that don't want to pay money for games:

http://www.1up.com/do/feature?cId=3165201