Interesting topic.
I was just trying to upgrade mine.

My view..
--Service is very important
--It will help a lot if you have some knowledge about it as well.
--Do not be too cheap also.  Bandwidth can cost you a lot.  Google is loosing money on Youtube mainly due to the bandwith.
--  Consult with an expert also.
It also depends on what you need it for?  In my case I run for just one website that takes lots of resources.
Choosing the right server can also be confusing since there are many choices/configurations.

Yes Rackspace is well known but there are others that are good too.  Try to deal with those who knows a lot about dedicated hosting.  For example, I wouldn't go with godaddy.

By the way if you want lil cheaper option then you can try VPS as well, but it really depends on your need.

I will be more than happy to discuss with you on this matter.  You can email me via sajha.

Good Luck.
Nischal.