I appreciate the willingness to give gymnastics a nod. I'm INCREDIBLY biased, but I have to go with gymnastics as well. I just got back from Beijing and while I was there I went to men's gymnastics (3 sessions), Men's Volleyball, Women's Beach Volleyball, Men's Water Polo, and Track and Field.
I had an amazing time at the track events - just like Dana said, all the events are incredibly exciting. I couldn't care any less about the Women's Heptathalon generally, but you wouldn't have known it by how I was yelling at the event. Also, the bird's nest stadium is the most beautiful stadium I've ever been in.
On the other hand, I couldn't help but to be struck by the narrow nature of some of the track sports. For example, I religiously watch the 100m sprint races and respect them as athletes, but there's just not that much to it. For those people, it's a full time job...9.69 seconds. The analogy I drew was that it would be like gymnastics being turned into an iron cross contest. Instead, there are 6 distinct events (for men, 4 for women) that all require a relatively discrete set of skills.
Anyway, that's all for now...I'd love counter arguments