Tom Brown park has a lot of great areas. There are courts, courses, fields and playgrounds.
One of the coolest features is the disc golf course. Buy a couple of discs over at Lofty Pursuits, and then you're all set. There are no grounds fees, tee times, etc. If you go on the weekend, there are usually really nice disc golf "regulars" who can help you out with some of the game basics, too.