If you ride mostly pavement, dry gravel roads and/or groomed chat trails, mowed levees, etc., take a look at Continental Cyclocross Speed tires.

Since last autumn I've ridden the wider version, the 700x42 Speed Rides, on my rigid mountain bike. Love 'em for the conditions I described. Smooth, quick and quiet on pavement, tough enough for bombed out cratered asphalt, plenty good enough for the gravel/chat trails I ride, and even enough grip to climb the grassy levees in our area and ride the levee tops -- as long as it's fairly dry. They aren't for mud or loose dirt or serious single track.

A couple of friends ride similar tires by another manufacturer but I can't recall the make/model at the moment. They aren't the Clement X'Plor. I've seen 'em on the racks at REI and Mellow Johnny's but the name escapes me. Anyway, they're similarly designed for dry cyclocross, pavement-friendly, with just a bit more of the diamond or file tread than the Conti Cyclocross Speed and Speed Rides. Their tires also feel a bit heavier, thicker and possibly tougher, but they cost a bit more. The Contis are a great value, especially the Speed Rides from Jenson USA.