There are a lot of crank brothers haters out there - they have overhauled the designs recently making a lot of improvements, I found shimano crap on balance.
There are a few things to consider:
Do you want a cage or platform or just the clip part
What are you going to be doing in them
What sort of shoes do you want
I have used the Specialized BG Comps which give a reasonable amount of stiffness and normally use them with a smaller pedal (CB Candy - 5 year old good as new) The stiffer shoe means you can run a smaller pedal.
I also have some 5.10 Minaars which are a flat skate style shoe with a clip. I use these with CB Mallets in order to have a bit more support and so that I can get away with dabbing, starting, riding DH. They turned out to be comfy so I keep wearing them. They work well with the bigger pedal and the Pins (Note non of the shimano pedals have pins) There are also some Teva clipped shoes coming out soon.
Thats the general advice, I found my spec shoes lasted a year with a lot of riding but that was fine really as I abused them. The Plastic sole type shoe doesn't like walking/scrambling through rocks etc. The Flat style doesn't work well in mud.
The other up side of the CB designs is that they work perfectly well in mud ice an snow as the mechanism stays clear.