Bought an iGo adaptor and the Invisible Shield. Also upgraded my car stereo to an iPod ready deck. Sides that, I don't really think anything else is real necessary, but a lot of things are sure fun to have
Case and screen protector for peace of mind.
Nice headphones.
Car iPod connectivity so that I can control listening to music via steering wheel buttons and have song info displayed on radio screen.
Home iPod connectivity so that I can listen to music on the nice home theater system.
I have a car charger, case, screen protector, and the apple care extended warranty. It came as a discounted price when I upgraded my phone so I though why not just do it.