From the responses, it sounds like pushing is a reasonable next move. That's what I did.

The SB called instantly and turned over pocket 99. Turns out, he caught the last 9 in the deck. The preflop raiser and the guy who moved all in on the flop before me turned over J9o.

The hand stacked me for the second time in 30 minutes (see thread "Playing the Turn"). I left the game at that point, figuring that this was not my night.

As I usually do, I thought about the hand afterward to consider whether I had played it poorly. On the flop, I think my only options were to go all in or fold. If I just called, there would be $400 in the pot, and I'd have only about $100 left behind. Not only would I be giving the right odds to the SB to call if he had only a heart draw, but I would have to call with my remaining stack no matter cards fell because of the pot odds. Thus, calling didn't seem like a good option.

I never gave any serious consideration to folding. I had top two-pair, and I felt that if someone made a set, they would have to show me. The SB did. I hope my thinking wasn't stupid, but if it was, I'm willing to hear it to avoid making this kind of mistake again.