Mountain wave is indeed amazing stuff. On Febuary 17th 1986 Paul Harris, flying out of California City Airport, climbed in mountain wave generated by the Sierra Nevada mountains to 49009ft to claim the absolute altitude world record for a glider.
Well known (and very wealthy) aviation nut Steve Fosset is planning to break the record and eventually reach 100,000ft with his Perlan project. Check out:
http://www.weatherextreme.com/perlan/ for more info.