There are a number of great resellers that can offer you fully managed servers from all of the main server companies. If you’d be a little more specific as to what you’re looking for, the people here will have an easier time narrowing down some great options for you.
Are you just looking for a company in general that offers managed (or fully managed) servers at a good price, and on a solid network?
At a glance, I'd say you should go with a Server Matrix or GNAX reseller.
If you need it "fully" managed to the point where you yourself don't have to do anything, then I suggest going with a reseller that offers fully managed servers. Usually that's cheaper (if you go to the right place,) then hiring an additional person to admin the server for you. Or at least that's what I've experienced.
If you don't need it "fully" managed but something like Server Matrix's basic management package would work for you - then unless you're looking for the cheaper pricing a reseller can potentially provide you with, I'd say go to either www.FastServers.net,www.GNAX.com, or my fav, www.ServerMatrix.com.
I'm sure you can find resellers to all of those companies in the offers section. Or just by having people contact you.