I just put together a page with links to all those special "do anywhere" caches. Some of these caches stretch the usual definition of a typical geocache, but I think they're fun anyway.
I've particularly enjoyed the Benchmark Recovery cache and have found several of them around my area; although I only logged the cache as a "find" once. =P
Anyway, enjoy:
http://www.brillig.com/geocaching/special.shtml
Please let me know if you know of any that don't appear on this list.
Thanks!
-Buxley
-- Ed Hall (edhall@brillig.com) http://www.brillig.com/ "There's a hell of a universe next door: let's go!" - e. e. cummings