I’ve tried a few browser bookmark syncing services in the past, but I’m really impressed with Foxmarks, for their Firefox, Safari, and IE support.
As a bonus, once I set up foxmarks for Safari, and then synced my iPhone, my firefox bookmarks transferred to my iPhone.
Lifehacker recommends an app, O-Marks, for using foxmarks to sync your bookmarks over the air:
http://lifehacker.com/5051271/o+marks-syncs-your-foxmarks-bookmarks-to-your-iphone
But I find just opening up Safari every once in a while and syncing the iPhone works well enough for me.