I ride on 700x25's. I strongly recommend getting a Gatorskin type tire. I got a pair for my bike this summer after spending every other ride last summer changing flats. I had a rocky start with the GatorSkins this spring with a couple flats but have since been flat free. I ride on some really trashy shoulders 5 to 6 days a week. Being flat free is saying alot! I also use Slime tubes.
Don't be afraid to change a flat! Just practice a few times at home. It's not that hard, just a little messy if you're changing the back tire.

bikerHen