Crackdown
I've re-uploaded the pics in the old post
(here), they weren't working anymore.
Crackdown 2
I really can't find an higher res version of the cover artwork :/
1. 1200 x 1636
2. 3738 x 2483
Cranium Kabookii
1. 1563 x 2223
Crasher
1. 4034 x 2852
2. 4034 x 2852
Cruis'n
1. 1470 x 1800
Crusader Kings
1. 2669 x 3422
2. 4969 x 3995
3. 3559 x 1524
Crusader Kings II
1. 5440 x 7680
2. 8326 x 11869 (higher res and slightly different aspect ratio compared to pic n.1)
3. 8419 x 11906
4. 2444 x 3337
5. 1612 x 2052
6. 4724 x 1524