Welcome to the forum drich...
As to your questions--The Denon 989 is the model equivalent to the 2809ci, the model number is different only because these are sold at major retail locations like Circuit City. This is the newest model in the '28' line following up the 2808ci--this unit retails for $1,200. The 3808ci is the step-up model in the Denon line and retails for $1,600. I do have a bias for the 3808 as I own one, however it really is a fantastic AVR.
Despite the price difference, I would definitely go with the 3808ci over the 989 in terms of the amplifier, connectivity, and especially for the GUI menu support the makes set-up and tweaking a breeze. Of course, it all depends on your room, number of components, listening habits, and needs that will dictate which AVR will be right for you....But for the $190 difference the 3808ci is certainly worth it....