I am not gonna make a massive post about this, but i came across this browser this morning which looks pretty cool.
Basically some guy over at My DebugBar has created a little browser which allows you to switch rendering engines between all versions of IE from 5.5 up to IE8 Beta.
I am fully aware that there are other programmes out their that allow you to install multiple copies of IE, but this little beauty lets you change the rendering engine by just hitting a drop down box so you have everything in one place.
Of course it only works on XP and Vista, but should save people some time. I however long for a OSX version of this software as running IE6 in an emulator to test pages really sucks.