First, you shouldn't be using IE as your default browser. Use a modern browser to do your testing in. You can then go back and fix for IE's broken layout model. If you're on Windows, Firefox is your best bet. If you're on a Mac, Safari or Firefox are great.
You should test in every browser you can get your hands on though - and on various operating systems. My testing suite includes IE6, IE7, IE8, Fx2, Fx3, Safari 3, Safari 4 Beta, Chrome, Opera 9 tested across Win XP, Win Vista, Mac OS X Leopard & Linux. We've also started to test some of our sites in various mobile browsers.
Really, there are a lot more compatibility and accessibility concerns than testing in 3 browsers will reveal. If you're serious about reaching a wide ranging audience, you need to be thorough in your testing.
Bookmarks