Bowtie
Mac
Bowtie is a free application that allows you to control iTunes and your iPhone (requires 99¢ companion app) with customizable shortcuts, submits your songs to Last.fm with support for Loving and Banning, and sports a very simple, yet very powerful, html5 + css + javascript based theming system.
iPhone
Bowtie for iPhone is the opposite of Apple's Remote app: Imagine you're sitting in your living room, listening to your iPhone on shuffle on your terrific new speakers, when a song you don't like comes on. You could get up, walk across the room, and press the Next button. With Bowtie, you don't have to.
Available on App Store for 99¢
Requires iPhone OS 3.0 or greater
Windows
Bowtie Remote is a free application that allows you to control Bowtie for iPhone with a beautiful album artwork display. Now, even Windows users can control and enjoy their music without leaving their comfy seats. This app requires purchase of Bowtie for iPhone in order to be at all useful.