Well, I typically delete what i'm not going to return to, or not actively playing. This is what's installed right now:
Open Transport Tycoon Deluxe (not actively playing)
MineCraft (not actively playing)
Skyrim (not actively playing)
Mass Effect 3 (done)
Diablo3 Beta
Path of Exile Beta
Legend of GrimrockI was looking at Path of Exile to tide me over while waiting for Diablo 3, since I'm not going to play the beta any more right now, but it's just not quite right for me. I can't stand the economy of the game, and the excess of unidentified items really pisses me off as a result. I'm going to uninstall it as soon as I'm typing this post.
I'll end up playing LoG until D3 drops, although if I've not finished it by then, I'll need to wait until I've cleared at least one character through to end-game in D3 before I even think twice about picking it back up. We'll see how that goes.
I'm holding out for the revised ending for ME3, but once I've played that, I'll likely can it. I'm going to keep Skyrim around for a while too, since there's so much new content being created... but again, unlikely that I'll even think about touching it again until I've run through D3 a few times. OpenTTD and MineCraft are lost causes at this point, they're just not too big, and haven't bothered to clear them out since I've got saves all over the place.
What's next, other than Diablo3 (obviously)?
Likely Boarderlands 2, BioShock Infinite, and Torchlight 2. I love the BioShock series, and I can't wait to play Infinite. Boarderlands was made significantly better with all the DLC (and this is how DLC should be!), really stoked to play the second one. I'll play Torchlight 2 after all of the rest, and out of obligation only. Had it dropped before D3, or even LoG, I'd likely play it through first... but they've missed the boat, and I'm quite disappointed.