These are all the officially-released codes I am aware of. I do not post codes obtained by cracking the game. (Nor do I know any, so don't ask me. I'm not kidding.) I only post codes that have been officially released by Cartoon Network, so I also don't post codes obtained by guessing. Don't send them to me.
Aired during the 11/9/06 7:30 showing of I Only Have Surprise For You:
OWLFLY
Gives you an owl buddy
Aired during Podcast 14 on cartoonnetwork.com:
CREATE
Gives you a Craig McCracken buddy
Aired during Podcast 14 on cartoonnetwork.com:
BIGTOE
Gives you a Bigfoot buddy
On back of insert that cames with the Season One Foster's DVD set:
DVDBUD
Gives you a school of flying fish buddy
Shown above the game itself on 4/2/07:
IGLOOS
Gives you a frozen dinosaur
Shown on 4/2/07:
TOASTY
Gives you a bonfire "rug"
Shown on the Cartoon Network site on 4/03/07:
CANVAS
Gives you a caveman painting
Shown during Bloo's the Boss on 4/03/07:
ROCKON
Gives you a stone floor
Shown on 4/04/07:
EGGLIT
Gives you a dinosaur egg lamp
Shown on the CN Podcast April 6:
VROOOM
Gives you a prehistoric chair
Shown on 4/09/07:
HOLLOW
Shown on 4/10/07:
RIBBED
Shown on 4/11/07:
FOSSIL
Shown on 4/12/07:
HANGER
And some codes I don't remember where they came from:
QUARRY
CAVERN
ELDEST