OK...which bigs are most worthy of playing in the NBA? Obviously, not the ones already under a team's control.

In the interest of full disclosure, I'm a Sixers fan, and I am looking for a halfway decent defensive C or PF who can rebound. Although Spencer Hawes has been a bit better than expected (he hasn't been putrid lately), there's no even passable backup.

And they desperately need some decent size with defensive ability. 

I know the Sixers don't believe in the D-League, but I do (like that matters) :)