What road tire should I buy for my new cyclocross I'm a recreational rider wanting to get more serious with cycling. I like Cyclocross bikes for their versatility and plan on commuting to work using my new entry-level Nashbar CX1. I've heard that knobby tires can be pretty rough on the road so I'm looking for a pair road tires to put on. What size should I consider? Some people use 700 x 30 while others recommend 700 x 32 or 700 x 33. What are the differences between these specs? Thank you all in advance.
It really depends on how much your budget is. Usually tires with lower rolling resistance comes a bit, if not alot, more expensive. Sk if you are just going for a pair that's cheap. I think it's best if you go for a 700x30. Since this one has the least amount of tire against the road.

I'm also trying to figure out why you don't want to invest in another set of wheels for commuting? Which in that case would mean you can try a road bike tire. A 25 or 28 road tire wouldn't be bad for a cyclocross bike, and I guess it is also ideal for local urban commute.

Again, it is up to you.