I was working last night on a box model explanation, and I decided that maybe a list of browsers that you can run 'side by side' on your computer would be useful to people.
Until recently, this list would only have included one version of Internet Explorer. Now, it includes versions 3 to 6. How? Well, someone called Ethan Marcotte wrote a tutorial on how to alter the programs to make them run in parrallel. Then Ryan Parman of Skyzyk.com completed the tutorial and offered the files as downloads form his site: read http://www.skyzyx.com/archives/000094.php for the complete low down.

So, moving onto other browsers:
http://www.mozilla.org/products/firefox/ - Firefox, an excellent browser, offering tabbed browsing support. It's also free. Netscape browsers are based on the mozilla core.
http://www.opera.com/ - Opera - the free version displays banner ads.
http://www.avantbrowser.com/ - IE but with tabbed browsing.

For a pretty much comprehensive list of browsers available for download, past and present, visit http://browsers.evolt.org/: