There's a good guide to the rad powersets here.
I have a grav/rad and posted my build up here. There are helpful comments about slotting, etc., on there.
The debuff toggles are fantastic. Everyone will love you for Accelerate Metabolism, Fallout is only useful if you have faceplanty teammates, and the others I haven't tried personally. Hope that's helpful! 
I don't have any problems with the earth side cause I played another earth controler to lvl 38, but im compleatly clueless about the rad side. What powers, what to slot, what, what, what.