As far as I know WHT hosted on the Rackspace.com. I have a guess that V7 and DP forumds might be hosted there as well. Hope John answer that soon unless he keeps that in secret
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As for forum recommendations. I think that it depends ... on your forun size, software you have been using for forums etc....
I suggest you have a look at Serverpoint.com (they have separate offer for forum web hosting) or Santrex.net (they do not offer forum hosting separately, but have rich choice of web hosting packages).
Also software developers often post their web hosting recommendations on their web sites. Check that way as well.
Good luck