The first time you press a button in Ghostbusters - assuming you run straight to the fire pole - you get 5 Gamerscore. Plenty of other games will fatten your total for not much work.
I haven't played Prototype, haven't played Red Faction: Guerilla yet, but of the new games out there I scarcely see how any can give you as much in a single, no-frills playthrough of the main story as Ghostbusters did. You'll get 110 for sleepwalking through the first level, 125 if you zap the ham and get knocked down by your own proton pack. Beating each stage also returns another 20 Gamerscore. These things don't take the word "achievement" very literally, IMHO.
If you're looking to finish off Father's Day weekend with some good old-fashioned achievement-whorin', TestFreaks Blog has a long list of titles, both retail and XBLA, that can prop up your overall gamerscore. You may have some laying around, who knows. But if anyone's got a recent game that offers as much score for as little work as Ghostbusters, let me know in the comments.
The Ultimate List: Best (And Worst) Retail & XBLA Games to Boost Your Gamerscore [Test Freaks, thanks Kristofer B.]