The A-lister for dedicated servers is Rackspace, a managed hosting provider I'm always happy to recommend. Great support & service. The one "downside" is that their price reflects their quality.

For cheaper dedicated boxes, you have to sift through hundreds of hosting companies and try to find ones who meet your needs, aren't going to screw up, and support you to the level needed. Sometimes you don't need a lot of support or uptime, and so you can get away with a cheaper box. I read some good things about ServerBeach and LayeredTech -- they seem to be a popular choice for inexpensive dedicated machines.