Personally, I use
http://ev1servers.net I've heard of people using
http://www.futurequest.net but I don't have any personal experience with them.
You should also inquire any new hosts to make sure they have the necessary support for the Next product, assuming you are wanting to upgrade to that. The preliminary info released about the new product states MySQL 4 as a requirement.
Another place to check about UBB Friendly hosts is
https://www.ubbdev.com/ubb/ultimatebb.php/forum/11.html There is honest feedback from UBB Users.
