So I’ve been playing Alter Ego lately and it made me hungry for some new, unusual web games. I know all about Bejeweled, Line Rider, and the like. What I’d love is some suggestions for obscure games I might not have heard of before.
Have you looked at Tranquility?
While it might not exactly be obscure, it certainly is fun.
Online flash version of Portal, based on but not affiliated with the game by Valve
Found this one tonight and I love it!
Thanks for the suggestions guys. These’ll keep me busy this afternoon. Goodbye, productivity ! 
Several of the games mentioned, plus a ton of others can be found on Kongregate.com. They have a great list of flash games.
The Tall Stump is a good one.
You want to Grow.