I've done many Crazylegs runs in Madison, WI (5 mile), the Meriter Nurse's Run in Madison (10k), the Bellin Run in Green Bay (10k), the Noodlini Run in Green Bay (15k), and the Seroogy's Valentine's Day Run in Green Bay (15K).
Crazylegs is the king. It's great for beginners and it has a laid-back party atmosphere. And free beer at the finish!!!
The Bellin Run in Green Bay is also a blast. http://www.bellinrun.com
Update 6/6/10: I did the 15K Noodlini Run in November, and the 15K Seroogy's Valentine's Day run a few days later. I got a first-place trophy in the Clydesdale division! Clydesdales are men who top out over 200 lb. I like to think of Clydesdales as the "true athletes." I'm not fat....
Our daughter was born March 14, and of course I stopped running cold turkey. I blew off Crazylegs because I would have been discouragingly slow. Trying to get back into it now...
Update 11/2/10: Currently training for the November 28, 2010 Noodleini Run! Kid #2 (Nora) wasn't as big a setback because I knew what to expect and I'm better at managing my time.