I went up with a friend in a tiny 4 seater plane in the summer. Probably one of the most exciting things I have ever done in my life. You cant understand it until you're up in the air...
I got a ride in a six seater many years ago in the Catskill mountains and it was a great experience (although I nearly vomited twice on some of the dips...).
I would love to do it again.
This past summer my brother and I were in the White mountains of New Hampshire. I asked a nice pilot there if we can pay him for a ride around the mountains but he said he couldn't do it because his insurance (which is apparently very expensive) wouldn't cover us. He didn't think any of the other private pilots would do it either for the same reason.