I highly recommend TireRack.com for tires. I bought some tires from them last summer (pre-Xfire days). I ordered some Pirelli A/T tires for my Jeep at lunch on a monday, and received 4 tires tuesday morning. Had them installed at a Firestone for about $50. The shipping was only $35 i think... which is less then the tax i would have had to pay if i bought them in state. The tires i bought were top-of-the-line, and were less expensive then the no-name tires at Discount Tire.

I was very pleased with TireRack.com ... I plan to buy my X-Fire replacements from them in about a year or so.