-- latest deal for a game through Steam that I picked up. I grabbed Dishonored and Doom 3 BFG together for $15. Would have been a better deal for me if I didn't have most of the other games. I think Disohonored has been available for $20 at its lowest for consoles.
The funny thing is though, that the 'best' deals I see on games for PC are the smaller indie/XBLA type games. Where the same game on Xbox Live will keep a 10-15 price indefinitely they're soon available on sale in Steam for under $5. And of course there are the Humble Bundles if you want those types of games even cheaper.
For example I got Renegade Ops with its DLC for $5.50 (main game was $3.74) whereas all that costs $18 or so on Xbox. I guess Renegade Ops was on sale down from $10 to $7.50 for the main game on Xbox last week, and I think that's probably as good as it got, still twice as much, and I don't think the DLC was on sale.
Though I did get a couple of hundred dollars worth of Xbox funny money for 2/3 off, so I guess everything on there is on a pretty good sale at the moment
. Still, I'm waiting for sales on games I want, and it's generally not as good as what you'll see on Steam. Spelunky is 50% off, but the DLC isn't on sale. Still I will pick it up since it sounds like a great game, almost snagged it at full price last week.
Whatever system you're on, if your patient you will eventually get good deals. But the Steam deals are more frequent and plain better 90% of the time.