Thunderstrike is generally nice. 6 pieces gets you a nice boost to ranged defense.
If you've got any defense powers, Red Fortune is fairly affordable if you look for deals on lower-level recipes. I put this in Maneuvers, but it can also go in the Black Scorpion patron shield. It adds some extra defense and 5% recharge.
Generally, I'd look for sets with individual pieces under or around a million infamy that give recharge, recovery, or accuracy bonuses. Rad/ has great defense debuffs that help your attacks hit, but you have to land something first.
When you get a little money to play with, I'd recommend 5 Positron's Blast in Nuclear Bomb and Neutron Blast, 5 Obliteration in Irradiate, and the Achilles Heel proc in each AOE. Playing an Earth/Fire dom with Achilles Heel in Quicksand and Stone Cages really gave me a new perspective on it, and adding it to my Rad/Kin AoEs has resulted in much maniacal cackling.
... that are affordable?
Even better, "earnable" by using AE tickets and cheap 'Bronze" random rolls? (I'm 42 now, but usually roll in the 35-39 category because I hear that has some of the best recipes.)