Very, very flat and scenic...28-June Menononee River Century. It is a little north of Green Bay. Nicely run, considered worth driving for.
Other than that, I'm located south so I'm not familiar....but you might want to keep an eye on the events calendar at the wisconsin bike fed (bfw.org). If you race, there are now two multi-stage race series, one before and one after the 5-july. The bike fed site references them both.
Or, grab a route sheet for the Door County Century and do a self-cater. Nice route.
The Fox Cities Cycling Club in Appleton does rides every Wednesday evening, as does the Chain Reaction Cyclery shop. Chain Reaction Cyclery also hosts rides on other days of the week (see the web site) and last year had informal weekend rides.
The Fox Cities Cycling web site also has maps online for local rides.