Moved the tread to get more coverage...
What format(s) are all your books in? Right now, the reader with the most format support with little to no coversion is the iLiad. But it's price (~$700) is a major deal breaker for most.
The cybook gen3 looks to be pretty open and they hope to support as many formats as possible. It should be out within 2 months. You may want to watch the forums and wait for more details.
The sony reader is your last option, but it has pretty limited format support, and most things require conversion to look good. With a large collection, it's probably not your best choice.