I was at a second hand store, and saw a copy of half-life for 2.99.
It was game of the year edition, which comes with Team Fortress Classic. I installed it, and thought "This game is pretty old, what if its code isn't used yet for steam?" and proceeded to enter the code.
It ended up being a bundle of ALL ORIGINAL VALVE GAMES.
Half-Life,
Counter-strike,
Day of defeat,
Ricochet,
Team fortress classic,
Half-Life: Deathmatch,
Half-Life: Blue shift
and Half-Life: Opposing force.
I'm having good luck at second hand stores lately.
Oh, and I got the source filmmaker beta.