I didn't unlock all CG and 4koma yet. There are probably quite a few hidden CG's in the game that you can only access by triggering certain side-dialogues (side-dialogues = dialogues not required to access for completion of the game). For example, in the third video you should see a CG where Ed and Al were sparing... That one can be triggered during the party, and you can only get that if you had Al talk to Ed at a specific time and place. There are probably other ones hidden like that too; I haven't tried yet.
As for the 4komas, they are unlocked as you beat the game default high score of the mini-games (you can access the mini-games for beating default high scores during the second run-through of the game). I didn't beat all of them yet... as they pretty much require you to beat the mini-game perfectly without any mistakes.
1 - http://www.youtube.com/watch?v=u_i0QzXBzZI
2 - http://www.youtube.com/watch?v=NUgIPWd3Coo
3 - http://www.youtube.com/watch?v=sXLQe_xawOc
You can probably see why I hate Elena from these? =P