ITunes and iPhone come together with this freebie. Possibly the coolest free app available in the iTunes Store, the Remote application turns your iPhone (or iPod touch, for that matter) into a wireless iTunes remote. Jaws will drop when you pull this one out to DJ at a party.
Note: This link takes you to the vendor's site. From there, you can follow the link to the iTunes App Store, where you can download the latest version of the software.