Your iTunes collection may have the Library of Congress green with envy, but when it comes to hosting its entirety on any computer but your own, it's about as mobile as Strom Thurmond. Make all your mp3's available from any comp, with blueTunes.
Ultra-simple and just released in beta, bT loads your music library onto its online database, then streams it back to you wherever you are, letting you mix on the fly the potent dancesanity of your "iPod Commercials" playlist. Set up an account, and blue's proprietary compression will cut upload times to seconds per track (those already in bT's database're skipped), so even sizeable collections will be fully catalogued within minutes -- or, the time it takes T.I. to release seven new must-have tracks. The first GB of storage is free, but upping your limit to anything from 5 to 40GBs only costs a few dollars per month, a blessing in disguise, as that money was otherwise earmarked for downloading Meco's disco "Star Wars Theme".
In the coming weeks, blue aims to support all file types (currently mp3-only); eventually they plan to allow you to download your tracks, backup that'll protect your collection from terrorism by angry friends who wish you'd stop blasting John Ashcroft's "Let the Eagle Soar".