My favorite accessory is the BudCozy. It’s a fabric cover for earbuds that keeps away thetangles and looks great too.
Battery for iphone:
This is the one I have:
http://www.batterycity.co.uk/sanyo_eneloop_mobile_booster_aa_eneloop_charger__incl__2_pcs__sanyo_eneloop_aa_-p-951.html
It has 2 AA batteries that can be swapped out. I got mine in japan. But I think you can get it in costco.
Here’s a bunch of power-related accessories:
http://store.apple.com/us/browse/home/shop_iphone/iphone_accessories/power?mco=MTU2MzM4NA
His and hers iPhone charger:
http://store.apple.com/us/product/TR330LL/A?fnode=MTY1NDA0MQ&mco=MjQzNTIyNg
Another external battery:
http://store.apple.com/us/product/TR823LL/A?fnode=MTY1NDA0MQ&mco=MjQzNTIzNg
And the Navigon iPhone app has is a better GPS than the Garmin i’ve used a number of times.