Claymore. So they can continue the manga story. But they better start the season before the last 3 episodes of the 1st season.
Black Lagoon. Well there's gone be another season soon but i want another and another and another and another. Well you get my point. You can never get tired of this anime. Also it's not just a big story that will be ruin if they make lots of sequels. Is little stories so they can make as much seasons as they want with no problem and i wish they do.
Ghost in the Shell. I wouldn't say no to Ghost in the Shell SAC 3rd GIG.
Another Full Metal Panic would be nice. Not that am crazy for another season but it's enjoyable. Except if it is another season of Fumofu. Then i really want another one. I had so much fun watching it.
And Baccano too needs another season. I really felt like i needed more episodes after the end.
And off course for crying out lout make a second season of D.Gray Man. How can you end it like that? We need to see the full story animated NOW!
Fruits Basket - seems like it just stopped
Inuyasha - same as fruits basket
I My Me! Strawberry Eggs - Had good enough ending, but would have liked a happier one. =P
Elfen Lied - Sad ending
Karin - It's my my favorite anime and couldn't think of another to put, soooo... (Though not sure, I was quite happy with it's current ending. Would just like to see more xD)
elfen lied has to have continuation!
Zero no Tsukaima 4 - also would be good
Seto no Hanayome
I've not ended Code geass R2 yet, but R1 is best and I would be able to watch 100 series of it ;)