It's been a few years since I went through the Thief series and I would probably play them again only if they were given a graphical update (and the medieval Ghostbusting missions from Thief 1 removed) - I'm not pro-graphics, but I would like them to be "remastered" professionally. The only games though that I replay, of the past 15 years or so, on a regular basis is Transport Tycoon Deluxe (in the form of OpenTTD) and Diablo 2: LoD. Semi-regularly will be various adventure games of old. And freeware titles too.
I did have a brief dalliance with going through the original Deux Ex for the umpteenth time and gotten as far as Hong Kong before getting bored, and managing to pull myself through Invisible War...*shudders*
Anyways, as for modern games? I'll probably replay the TellTale adventures and go through Psychonauts again.