Follow up:
I called the water company on Friday and got the water shut off. Saturday I broke out my two big pipe wrenches and pulled the old valve off. It is a one inch, 90 degree valve. Flare on one side, and standard pipe thread on the other (NPT?)
Took the valve to Home Depot and was promptly told that they do not carry any valves with flare fittings. So, I decided to try a dedicated hardware store - Ace. I've actually run into this situation before - turns out that "home improvement store" =/= "hardware store".
Ace didn't have anything flared larger then 3/4". The sales guy I talked to recommended a plumbing supply store; "The plumbers friend". The valve was expensive ($30), but they had the valve in stock. The sales guy was ridiculously helpful. Small specialty shops rocks.
The valve went in without a hitch. because I'm nervous about the fitting leaking on the main valve, I hooked my air compressor into the cold line where the washer normally hooks up and pressurized the system to 50 psi. Then, I went around with a bottle of soapy water and a brush and looked for leaks. Figured if it works on tires, it'll work on pipes!
Anyway - no leaks with air pressure. We'll see if it holds up after I have the water turned on this Monday.