I'm playing freakin' Morrowind again. I had to install the face replacements and better bodies mod so that it looked more up-to-date, but aside from my favorite house mod I'm playing it more or less untouched. (Vivec Expansion doesn't count, it makes it worth visiting!)
I also started playing Freedom Force again, mostly because my kids get a kick out of watching it.
The Specialists Mod for Half-Life is also super-addictive. Deathmatch against bots has never been so much fun.
Soul Calibur II for X-Box remains a guilty pleasure as well.