Join Date: Aug 2003
Bikes: '03 Fuji Roubaix Pro; '03 KleinGi Attitude; '06 Soma Rush; '04 Surly Cross-Check; '06 Soma Rush; '07 Scott CR1 / Chorus
Like others said, 700x28 or even narrower will be fine.
If you want a tire that's tough and puncture resistant, go with a Specialized Armadillo or a Continental Ultra Gatorskin. I've used both in 700x28 on my commuter - the Armadillos seemed a bit tougher, but the Contis seemed to roll better.
If you're interested in a bit narrower, I've had good luck with 700x25 Michelin Carbons.