Using iPod accessories with your iPhone

One of the most surprising things about iPhone is how well it works with the occasional gadget that was designed for iPod instead of iPhone. Today, I took out a box of miscellaneous iPod accessories and tried a few of them out with the iPhone. Some just didn't work. The Belkin TuneCommand A/V, for example, is meant for use with an iPod that supports video out. Others worked right away. The remote control shown here allowed me to control the iPod features of the iPhone including pause/play, track skip, volume control and so forth. The headphone adapter would not, however, fit into the iPhone jack without an adapter.

What iPod accessories have you successfully (or not) used with your iPhone?