$400 maybe $450. Not sure if you can get more on eBay. Apple stuff doesn't hold much resale value anymore, especially at the high ends.
This is because so many people have them now and many people upgrade more often than they used to, which means there's a ton more second hand Apple gear on the market than there used to be even 2 or 3 years ago.
If your strategy is to upgrade each time I would stick with the base models. They typically lose a lot less value percentage wise.
Example: you may lose 30% or 40% on a base model depending on how old it is, but a $100 storage upgrade gets you an extra $20 (80% loss), a 3G upgrade gets you maybe $30 more (75% loss), etc. and the higher up you go the worse the losses get.
AppleCare is also not much of a value add to most people looking for a deal on Craigslist and I doubt it would add more than $10 to the resale price (90% loss). Almost better off canceling it and getting a partial refund from Apple.
Also prices plummet when a new one is announced since everyone is trying to dump theirs and typically recover slightly (but not to same previous highs) a couple months later as supply goes back down for that model.
This is all based on my observations and experience buying and selling on Craigslist, through friends, etc.
Edit: I just sold my 32GB Verizon for around $350 and I was lucky to get it. Had it up for over a week on Craigslist in Chicago where there's a ton of people and I had only 2 offers, the one I took and a low ball offer, and a couple people wanting a trade for some other stuff I didn't need. Not like 2 years ago when I posted my original iPad for sale and got an email box full of reasonable offers.
I just wonder when people will officially stop believing/perpetuating the myth that Apple stuff is easy to unload without heavy losses. Maybe in another 2 years at which point the trajectory will match other products I guess (Apple is still higher than others at resale but the gap is closing fast).