off the top of my head:
PC
C&C 3 (i think)
C&C 4
starcraft 2
Dragon age 1, plus im sure i bought an add on that i never touched....
boarderlands - stopped as my save file got corrupted and couldnt bring myself to start a new character
xcom: apocalypse - the real time was good, but the game didnt feel as good as the original 2
ps3
wipeout HD
GTA4: vice city
Fallout 3 - got up to the last mission, but didnt want to 'end' the game, and never got round to buying the add-ons
Red dead redemption - stopped playing when i got fallout NV
Fallout NV - stopped playing when i got GT5
GT5 - well, slowly working my way back into it, although its mainly B-spec/online with mates
Gods of war 3
im sure there are more...
damn my lack of time due to a full time job