Games you bought more than once?

Arkham City and GTA 4. Both times they were on PC. They were both physical copies relatively close to their releases. Once GOTY or complete versions went on sale for ~$5 I decided to repurchase them through Steam, and replay through them!

Portal 2 - Xbox, PC

Batman Arkham City - Xbox, PC

As far as I remember only Ultimate Ninja Storm 3 (bought on PC again but it was the edition with all the dlcs) and Skyrim (got on PC the Legendary Edition)

Assassin's Creed 1 & 2 360 then rebought for PC when I got Red Ring and didn't have another 360 at the time. Plus I do like the AC Series (for the most part)

Blood 2... and Garry's Mod (bundle).

I bought lots of copies of many games for trade :D

Recent-ish games? Castle crashers, Tropico 3 + 4, on 360 and PC.

Lots of old Sega games, although I guess technically they were bought by my parents the first time because I was about 5, but I have given away multiple copies of some now (Sonic, Sonic 2, the bundle collections) purely because I think more people should have them.

Worst I've ever achieved:
OutRun 2 Coast 2 Coast. Bought it for PC, XBox, PS2 and PSP...

Medal of Honor (Physical, unsealed; Steam)

Gta Vice City, San Andreas and IV (ps2/ps3 - pc)
Darksiders I and II (ps3 - pc)
Saints Row The Third (ps3 - pc)
Bully (ps2 - pc)
Mortal Kombat I II III and 9 (ps2/ps3 - pc).... and I think thats all xD

Hmm... I'm sure I'll miss a few, but --

Physical and Steam:
Civ 3 and 4
System Shock 2
Anachronox
Morrowind
Oblivion
Divine Divinity
Deus Ex + Invisible War
Final Fantasy VII + VIII
Grand Theft Auto III + VC + SA
Max Payne 1 + 2
Midnight Club 2

And then some I owned on consoles:

Final Fantasy VII + VIII (yeah, I bought them three times)
Mirror's Edge
Grand Theft Auto IV

Probably missing a few, as well.

Blade Kitten came on out Steam recently and I bought that even though I already had it on PS3. They said they cleaned it up a little and tightened the controls. Plus, there's trading cards!

Bought GMod for a friend.
Who later turned into an asshole and stopped talking to me lol

Bastion - Xbox, PC
Ys: The Oath in Felghana - PSP, PC
Ys I&II - DS, PSP, PC
Final Fantasy VII, VII - PS1, PC
Final Fantasy III - DS, PC
Final Fantasy IV - SNES, PS1, DS, PSP
Final Fantasy VI - SNES, PS1, GBA
Tales of the Abyss, - PS2, 3DS
Phantasy Star II, III, IV - Have these on Genesis, PSP via the collection and PC, also have II on XBLA.

And when the Steam version comes out, will be getting Legend of Heroes: Trails in the Sky on PC, already have it on PSP.

Most of these I bought on a second platform for achievements or for more portability, in the case of Ys and Legend of Heroes, I just love the games that much and always support localizations of Falcom games even if I already have a version of said game.

Ys 1-2 and Felghana, PSP and PC.

Only Saints Row 2. Bought it first on PC, realized that was a huge mistake, then bought it on PS3 so I could actually play it.