I have talked to the powers that be at Blackhawk and they have agreed to open up their 60 acres to anyone as a "first time guest" to ride there with a member. I'm trying to get together a group ride out there. They have grills all around and could make for an awesome way to spend a day. Also it's the closest trail in existence to Madison, 10 miles from the capitol. Membership for summer bike trail use is only 20 bucks too, 10 for students.
There is a bunch of really really cool trail there both uphill and downhill, cool wooden features, plus a nice smooth grassy ultra low penalty beginner skills area with very small ladder drops, logrides, and ground level skinnys.
Also for experts this place WILL challenge your skills with a few different trails that scare me a little still. Also the trails are really just now starting to be developed with the addition of more xc singletrack this summer.