Ok, it was hard to find anything missing from the lists here, but I found some (and was surprised by a couple).
Firstly, I must once again mention The Journeyman Project series, though it has been mentioned before. They are collectively my "Best Game of All Time", so would love to see them here. Actually it would be even more amazing if GOG were somehow able to convert the JP1 remake 'Pegasus Prime' to work on XP/Vista, as it was only released for the Mac.
Anyway, on to the exclusives:
Conquest - Frontier Wars
Flight of the Amazon Queen
Republic: The Revolution
Can't believe no one mentioned the last two (according to the Search function anyway). In any case, I hope we hear about more publishers coming on board, as I'm having fun so far :).