I just use a logitech dock that has the little plastic inserts that will fit multiple models... I remove the plastic piece that makes it an exact fit and most any case will fit. It's not an exact science but it works.
[ame=http://www.amazon.com/Mobile-iPhone-Silver-Support-Calling/dp/B002OLM56K/ref=pd_sim_gs_e_1_2]Amazon.com: Elago M2 Mobile Stand / Dock For iPhone 4, 1G/3G/3GS, (Silver), Angled Support for Easy Video Calling: Cell Phones & Service[/ame]
I found this, one of the reviews I saw says it works with a case on the phone. But the review was from last year, so obviously the 3G or 3GS.
This is the one I use. Last year the switcheasy rebel case I bought had a special dock piece that worked with the case.... I wish more cases came with them.
this might work for you. spiderpodium.. i have one. it will hold any phone and case combo and you can snake the cable in the bottom to keep it charged. mine sits on my nightstand and works like a charm. in fact its pretty much universal and runs about 20 bucks