Ran off M-44 (black ice @ 50 mph) between GR and Rockford just before Christmas '08. Called American Express Global Assist to dispatch a tow truck and these guys showed up.
After hoisting me out of three or more feet of snow failed, he dug me out by hand! Eventually his truck was able to hoist me free. Ran me just under 70 bucks.
Pros: Prompt, affordable service