I've got a Reef Dynamics INS300 running my 300DD. I think it's rated for 450 gallons. They are no longer made which is too bad. It's been my best skimmer so far.
Whatever you get, I recommend getting it used and saving a bunch of money. Huge skimmers are expensive, especially new, but they are also hard to sell secondhand because there aren't nearly as many people with huge tanks.
this is a very good point. I did look at ebay yesterday to see what was out there. once I know what size of tank I am going with I will hit the for sale threads and ebay pretty hard.