wedgeski
Adventurer
Of those, I think Dark Sun would be the most interesting. Speaking as a Dragonlance fan, I think that seeting was mined for just about all it was worth in 3e; the concept of Ravenloft now appears to have become core, and in style; Spelljammer is a little 'out there' this early in 4E's run; and Greyhawk... meh, I can see it happening, but I don't anticipate it following straight after FR.
So, Dark Sun all the way.
So, Dark Sun all the way.