if it's for a closed loop, then work out what flow rate you want and get the most suited pump at 0' head. also look at the size of the inlet and outlet's on the pump - important to match your design. most are either 3/4", 1" or 1.5". restrict the inlet and outlets as little as possible (in other words, if it's a 1" outlet, match the plumbing to it. this will greatly dictate cost too as plumbing is expensive) if it's for a return, work out what flow rate you need at X head height. match the pump to that. iwaki RLT's are awesome for high head.
Reefonline.com.au are also expensive. ask her for a better price.