I fold...the only 2 hands you're really beating are AK or KQ, and given that he limped preflop at first, I'd be tempted to half rule out AK. I don't think you see KQ enough to call, even with 3:1 odds.

I suppose villain could be drawing with Q10 or AQ or something retarded and trying to get you to fold on the river...but I don't think that happens too often either.