Try Balance studios! It's right over the walnut st. bridge from west philly/upenn/drexel area between 23rd and 24 st. (it's about 20 feet north of Sansom street down a smaller street, I can't remember the name of it).

Anyway, the Ashtanga yoga classes are awesome! There is a Tuesday class at 7pm, a Thursday class at 6pm (I believe) and a 10 am class on saturday mornings.

Balance is also a Gracie jiujitsu school with terrific classes and really friendly students and staff. Both programs are led by Phil Migliarese. You can find more information on www.balancestudios.net

Hope that helps!