Bitcoinity's site is probably one of the better ones.

http://bitcoinity.com/markets

You need to watch the other US exchanges as well, not just MtGox. It's basically impossible to get USD from MtGox right now, making it a very poor benchmark for the actual exchange rate.

I think an HN person made this one recently http://pricebtc.com/

Yikes that totally is not working on the iphone.