Userscripts are great, but not everyone can use them. If you can, get and add Greasemonkey. Safari has CreamMonkey or PithHelmet, and Opera has userscript support built in. But what if you are using Camino? Or Internet Exploder? For these people, I introduce the GeekMonkey userscript injector.
Simply drag this bookmarklet to your bookmarks bar, and click on it while on any page that has a userscript on it. Any userscripts will automatically be turned into bookmarklets, which you can click anywhere you want.
After years of observation and reverse engineering I am proud to say I have been able to reproduce the IE6 algorithm to break even the most standards-compliant websites.
In my opinion, Xenocode Browsers is the ultimat tool for checking your website in different browsers. Xenocode Browsers allow you to lauch IE6, IE7, IE8, Firefox 2, Firefox 3, Google Chrome and Opera directly from the web. The only weak point: The service isn't available for Macs and GNU/Linux powered PCs.