B.,
I'm on my third baby now and I am DETERMINED to get this one right, so I am reading/re-reading all the sleep books we have accumulated having two not so good sleepers before.
The first word of advice (already stated here) is to put him to bed earlier not later. The books all say that fussy wakings indicate tiredness.
Also, stop going to him at night when he wakes - this can be a transition since it's something he's already used to. If you don't fix this now, believe me, it will only get worse. If you want you can go to him, but don't pick him up or get him out of bed for any reason. Slowly reduce your interactions with him at night - no touching, quiet talking, no turning lights on, etc. Each night, less and less attention. Eventually, not going in his room, but standing in the doorway and saying, "Goodnight sweetheart, it's time to roll over and go back to sleep."
Maybe you can reward him for staying in his room in the morning - something like chocolate milk with breakfast? Tell him Mommy and Daddy are still sleeping and he needs to play with his "friends". I agree that you'll need to change out the toys frequently.
I know this sounds silly - but it was something that FINALLY worked for us...we had "sleeping spray" (lavender linen spray from Bath and Bodyworks). My kids ask for sleeping spray when they are scared, sleeping somewhere unfamiliar, or just wound up. They have an aromatic trigger to help induce sleep. Our sleeping spray helps them "roll over and go back to sleep" at night because they smell it on their favorite blanket or pillow.
Right now I am reading "happiest baby on the block" - it might give you more ideas.
Sara
PS Feel free to e-mail me with any questions. Good luck!