Gonzo has 2 that he wears most, a black rolled leather collar with his tags, or his blue & orange nylon harness by Rogz.

Fozzie always wears his harness, I find it way more convenient for a puppy because he can't slip out, I can pick him up by it, and when he (inevitably) is pulling on the leash he isn't gasping for air. As I start seriously OB training him, he will start wearing a rolled leather collar. His harness is so cute, it suits him... it's a green/blue/yellow plaid nylon harness by Rogz.

Just to give them props, I love Rogz for Dogz! They have a bunch of cute designs & the really hardy plastic snaps have a "locking" option. They're also available at every feed store I've ever been to =)