I have both the Furman HDS-6 and the Behringer unit that was previously talked about. I think that thing was $99 when I got it. I hate Behringer stuff in general, but the headphone amp is pretty good. If you're not going to spend the amount that the Furman costs, definitely go with the Behringer.
If you can spend for the Furman, it is definitely the way to go. It relieves a lot of headaches when everyone can worry about their own mix. Once you get the hang of sending 1-4 aux's and a stereo mix, it usually goes pretty smoothly. One thing to watch out for though is that some people just can't get a good headphone mix themselves...I occasionally find myself helping tune in a good mix.