We go to the botanical garden at least once a month. They have all kinds of special things going on all the time, plus it's just a nice place to wander around and picnic.
Daniel Stowe Botanical Garden
Many of the local shopping centers have outdoor music on the weekends in the summer. I know Stonecrest, Blakeney, and Rivergate all have concerts on either Friday or Saturday evenings all summer.
Let's see...Knights baseball games are a lot of fun, and cheap too. Oh, and we go to the Whitewater Center almost every weekend too. You can hike, mountain bike, kayak and raft, or just watch the rafters. They have concerts every Thursday night there, and discounted beer and food too I believe.