Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
iTunes. Thanks to Apple's arcane business practices you don't really have a choice with the iPhone or iPad.
 
If you have MobileMe AND use Safari as your primary browser, that solution works well. If you do NOT use Safari as your primary browser you may need multiple tools to get the job done. For example, I use Firefox as my primary browser. I use Xmarks to sync my bookmarks, and Xmarks for Safari to keep Safari in sync as well. That then syncs to my iPod touch via iTunes.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.