A few of us Philly Robotics club members are working on quadrotors. I’m confident that once we have something in the air, other members will follow.
What is a quadrotor? It is a flying vehicle that is capable of hovering (similar to a helicopter, but with significant differences) whose propulsion system consists of 4 propellers (there are also 3, 6, and 8 propeller variants). Check out the videos in this link for an idea of what quads can do: http://fling.seas.upenn.edu/~dmel/wiki/index.php?n=Main.Quadrotor. (Members of the club were able to see a live demonstration of these quads at U Penn)
The good thing about quadrotors is that they are very flexible. You can build them completely from scratch from parts from Home Depot and SparkFun.com, rolling your own software. Or you can buy one ready to fly out of the box, or somewhere in between. There are very successful quads that were designed, built, and flown by people who know next to nothing about aerodynamics and control theory. On the other hand, quads are also used quite extensively in the top research labs (as you saw in the link above). Many technical papers are still published every year on aspects of quadrotor design and control.
You can get caught up on my quad development efforts here (along with bonus posts on quadrotor physics and control theory): http://www.rcgroups.com/forums/showthread.php?t=1284741. I hope Tom won’t mind if I link to his quad site as well: http://buildingdrones.org/. In the future, I plan to blog more here about the project, as well as post details on our Philly Robotics forum. You are always welcome to join us at our next meetup, the details of which can be found here: http://phillyrobotics.org/wp/?page_id=2