For commuting, finding a tire that wears well, offers some flat protection and provides good traction and comfort is a priority. As other have recommended, Gatorskins and GP4S in the 28mm width are a good option. Schwalbe Marathon Supremes are a little more substantial, and are well liked by the touring crowd.

For faster group rides (we're talking 26-27 mph cruising speed), you need a skinny racing tire. I used to use Michelin PR3, but now like Conti GP4000S in 23mm. Racing tires wear out much faster and puncture more easily than tires suitable for commuting.