I need a new PS3 game...

since u didnt tell us what you have already...

I am going to get GOW3 but it doesnt come out til Dec. 31. I have COD4 and Rockband. I was thinking of getting assassin's creed now that its on GH.

don't get assasin's creed unless you like doing the same thing 509230921309471023984023984 times. great story and concept, but i think they could have added a little more variety to it. here's a list of games i think you may enjoy:
1. little big planet
2. street fighter 4
3. killzone 2
4. resident evil 5
5. far cry 2
6. dead space
7. bio shock
8. ninja gaiden sigma
9. metal gear solid 4: guns of the patriots
10. rainbow six vegas (the first one)

as far as waiting for games to come out (i'd probably rent these just to test out the waters minus number 1 ):
1. god of war 3
2. singularity
3. chronicles of riddick
4. dante's inferno

thats about all i can think of off the top of my head.