You may want to look at ServerMatrix. They have a pretty good reputation in the Managed Dedicated Market. Reasonable prices, reliable network, and good support.
If you've never had a dedicated server before, I highly recommend going with managed and learning the ropes. Meaning, before you rely on "support", play around and see if you can fix it yourself. That way if you succeed, you've learned something new. If you don't succeed, then you have support to rely on.
I'd also recommend reading. There are many good resources around that help you take baby steps in system administration. The learning never ends..
Coming from Managed and/or Shared Hosting....unmanaged is a whole new ballgame. I'm not saying that to detour you away from it, but it's definitely not a walk in the park and there is much to learn.
Good luck in your search!
