I'll gladly pay full price for a game I know I'll really enjoy and want to play right away, or for a developer I want to support.
The rest of the time, though...my rule is always to wait for a sale, especially when it comes to buying stuff on Steam. What's offered now for $20-30, I can get for $5 if I play my cards right and wait for the next big sale.

Really, a few pre-orders aside, I can't remember a time I spent more than $15 for a game.
...And yet somehow, Steam is still managing to take all my money.
