Ok, now for my choices. Unlike many people on these forums I am not a fan of Druids so they are not in my list of suggestions. With that being said, I do agree that the Druid should be first, and Turbin has said the Druid would be the the next new class (no ETA however).
Scout - This is a Gish class meshing aspects of Rogue and Ranger. I really like the class and their precision damage was always easier to acheive than Sneek attack. All they needed to do was move 10' before attacking each round. They got less d6 than rogue but also gained bonuses to AC. Admittedly the "move 10' feet" mechanic would be unlikely to work in a real-time game like DDO so likely it would translate to Sneak Attack and an untyped (or dodge) bonus to AC .
Warlock - There has been alot of discussion about them so I'll not expand too much here. Unlike opthers I do not see them as watered down Sorcs. I do think they are unique enough to differentiate them in DDO.
Factotum - The true Jack of all trades. They get a specific number of inspirations a day spent to mimic other classes abilities. This would be a group of abilities borrowed for other classes that all have a common cool-down timer and draw from the same number of uses/rest. Problem here ballancing them against the other classes to make them usefull without being over powered. In PnP they used the Inspirations/day a limiting factor (like 8 at level 20 or so) but I think they over did it. I could imagine that instead of getting their own PcE's they would draw from the other classes PrE's.
A note on Artificers. I would have had them as my third choice because this is Eberron after all, but I didn't include them for several reasons; 1) They would have to implement a true crafting system to make this class viable (I am in favor of this but I believe many wouldn't be because it would require them to have the crafting feats and required spells to craft), 2) The class is heavily devoted to buff's but generally their buffs are done out of combat just befor you attack (this is due to the time required for many of their Infusions, so no refreshing buffs in combat on recently rezed alies), and 3) They also have an affinity to created Homunclus friends which none of the classes with friend like abilities have them (Familiars, Special Mounts, Animal Companions, etc...). Artificer would require some fairly heavy modifications to the gave to ba able to implement.