I haven't tried recently, but I know that Avant Browser (using the IE 8 engine) will work.
I believe MyIE2 (and/or an older version of maxthon) will work as well, but again, requiring the IE8 engine.
Also there's a portable version of IE8 beta floating around. It uses VMWare Thinstall. I am able to use it with IE7 installed, but I'm not sure how it will work with a later version of IE installed. The md5 hash is below.
I'm certainly going to hold on to it for that time when I'm forced to switch from XP.
c:\>md5sum -b "IE8 Portable.exe"
b5be2cf02d6aaa8f1321b66e0ba44cfa *IE8 Portable.exe
c:\>md5sum --version
md5sum (GNU coreutils) 5.3.0
I've also heard of another app called IE Collection. I'm not sure how it works.