I've always liked the Yoga that's kind of like gymnastics; a lot of the related stuff on that page is cool too.
I've wanted to be able to L-seat for a long time, and I'd love to be able to "flag" but that stuff is pretty far away for me still. The definitive site for this stuff is Beast Skills - all bodyweight feats of strength. Very inspiring. I'd much rather be able to say I can L-sit or flag or do a full rollout than say I can bench whatever number.
The first time I saw Cirque de Soleil, they had the standard two strong men act, where they do planche moves and balance on each other and all that, it blew me away, I got goosebumps. I think that shit is just gorgeous and so inspiring. The strong men act never gets much applause. Some stupid clown gets all this applause for being dumb, but oh two guys doing amazing hard beautiful things, meh, yawn.
Browsing Youtube for circus strong men acts, I find two interesting things. First, most of the clips of strong men seem to be posted by the duos themselves looking for work. Don't worry boys, when I get rich I'll hire you to perform at my crazy parties. The other thing I notice is that the strongmen duo acts have been embraced by the gay community. No surprise there and I certainly don't blame them, but the video of flames is a bit too on the nose ; and Les FarFadais are just one accidental slip away from gay porn. Now this is a good old standard manly strong man duo; I love the T planche they do around 3:00
On a semi-unrelated note, Cirque Berzerk used to do a lot of shows in SF but they disappeared for a while and have now resurfaced in LA. If you're in LA, definitely check it out. It's like a cool cirque with great acrobatics, but a bit younger, less cheezy, a bit more fun and edgy, not nearly as professional as something like Soleil but that's part of the fun, it's more intimate.