Most games I'll at least try for 10mins, but have yet to try the following games I own:
-Half of the ID Super Pack on steam
-Total War (not the Shogun/Medaevil/Rome series, this predates them) - free gift with an order years ago
-Prince of Persia: Warrior Within (free with a gfx card)
-A bunch of games I inherited from my sister, including Civ4 Complete, Mark of Chaos, NWN2, Morrowind, WC3 expansion, Baldurs Gate series, Icewind Dale series etc
-Football Manager 2009
-Mass Effect (seemed like a bargain at £9.99 a few months back, hasn't come out of the cellophane yet!)
-GTA4 (to be fair I only got given that yesterday, and I don't think it'll run too great on a Geforce 6200 PCI!)
-Peggle Extreme (getting tempted as I was hooked on Bejeweled by the same developer not so long ago)
I'm placing an order for Project Snowblind this weekend (only £2.48) but no doubt that'll sit around unplayed.
I'm far worse on the Wii however - I haven't opened Zelda Twilight Princess yet, despite buying it the same day as the console nearly 2 years ago. Likewise we waited for Super Mario Galaxy and Mario & Sonic at the Olympics to come into stock, bought them, and yet never played. The Wii Fit stayed unopened in it's box for about 6 months before finally getting broken out a couple of weeks back after moving house.
So come to think of it I think we've actually only played 3 of the 6 games we own for the Wii!
I've got unopened DVD boxsets too. What I really need is to get made redundant so I can start making an indent into some of this entertainment stockpile!