Winamp, my media player of choice for mp3, is a proprietary program originally written by a company called Nullsoft (which has since been bought by AOL). Unfortunately, Nullsoft has not produced a portable version. Because Winamp is proprietary and because of associated licensing restrictions, reputable companies like PortableApps.com cannot offer portable versions. While there are any number of portable versions created by a variety of rogue programmers, they typically consume far too much disk space, and their download sites all impose a 60-second wait unless you pay for a faster "premium" download with no wait. Hence the need for a viable alternative. The following programs, while lacking all of the more elegant features of Winamp, nevertheless provide highly acceptable alternatives.
A small, light-weight, easy-to-use mp3 player that covers all the basics.
I have been using IrfanView for many years, and while I am not yet ready to abandon IrfanView, I suspect that if I had stumbled upon FastStone first, this might be my image processor of choice. It certainly has a more impressive, modern appearance. I especially like the unique feature whereby even if your photo's dimensions are greater than your current screen setting, FastStone's crop board reduces the image to fit your screen so that you always see the full picture for precise cropping, unlike IrfanView. And perhaps best of all, FastStone comes in a portable version.
The absolute best free image viewer - IrfanView - is now available in a portable version. Don't leave home without it! [Added 10 April 2011]
These two versatile programs that will play the vast majority of audio and video file types that you are liable to encounter.