Which hammer drill should I buy?
Cordless

I re-read your question and saw it said cordless. I don't have a cordless but this website rated the Milwaukee 0824-24 V18 Lithium-Ion Hammer Drill Kit as the best. The Hitachi DV14DL 14.4-Volt Lithium-Ion Cordless Hammer Drill is another quality product available for about the same price as the Milwaukee drill. 

Cord

I have this one and it works pretty well - Hitachi 5-Amp 5/8" Hammer Drill



Don't forget to buy a good hammer drill bit if you are doing true hammer drill work! Non-hammer drill bits will break. I suggest carbide tipped drill bits for this task. The smaller the drill bit though, the faster they break - carbide or not.