If you're just trying to get a lot of preamps for a low price (which is a position you often find yourself in while in a band), the Behringer mixers are definitely there in terms of the price point.
Calico's got a point, though, about Mackies. For example, I had a 16 channel Behringer (with 8 preamps) that I always felt good about. Then I picked up a used Mackie 1604-VLZ (prices are good now that the PRO model came out) mainly because I wanted the additional 8 preamps. But the first time I ran it instead of the Behringer I was shocked at the difference in sound -- just from the preamps! It sounded clearer and better all round and required less EQ to achieve a great tone.
Anyway, I think if you're looking for the cheap in, the Behringer will do you. If you have the option, consider a Mackie, even used.
How many channels do you need, and how many preamps? What kind of output do you need?
Chuck