If you don't mind hills, I would suggest going west: maybe start at/near Riley Tavern and ride a big arc north toward Mazomanie and then back southwest toward Mt. Horeb. Imagine a giant triangle drawn between Verona, Blue Mounds and Mazomanie - there are a lot of good roads in that area. This might be better defined as the area between Hwy 151, Hwy 14, and County K, although there are a lot of great rides outside of those boundaries too.
You might plan to end up at the Grumpy Troll in Mt. Horeb - then your trip back to Madison will be mostly downhill, either on the Military Ridge Trail (boring, but easy) or on the road. I usually drive out from Madison and park at Pine Bluff or somewhere west of Elver Park.