[Brian462]

Here's my guess:

Either a weakish ace(AJs, AJ, ATs) or 99. If he is on an Ace then he might have checked after the blinds figuring you guys had nothing, hoping you might pick up a small pair and bet out. If he had 99 then he wanted to wait for the river to raise, figuring you didn't have much and were maybe even bluffing.

I'm probably way off though.