I would say isprime.com
But take a look at these companies. I don;t think you can go wrong with these. Watch out for all those wannabe hosts, that don't even own the ip's, have no access to the DC etc.
Also try the 24/7/365 support before you decide
www.isprime.com
www.natnet.com
www.swiftwill.com
www.oxeo.com
www.cavecreek.com
Andre