Free portable software for USB keys:
You can download a number of great portable software applications that run right off your USB key, with no need for installation.

The best one I've found to date is ClamWin Portable, an antivirus program that's detected viruses missed by AVG.

There are dozens available, including the complete OpenOffice Portable Suite, and all sorts of other file-sharing, FTP, graphics and other apps.

You can find most of them at the Portable Apps website at http://portableapps.com/apps. The site also offers an integrated suite of all the best apps bundled into a single application.