As a developer, can I safely upgrade to IE8 and use its IE7 compatibility mode to test how sites look in IE7? For IE6, I have a virtual machine and it is quite inconvenient. I d
Multiple IEs was listed in another answer.
There's a successor to "Multiple IEs" called Internet Explorer Collection that is more up to date.
Seems that Microsoft has finally released Expression Web SuperPreview
It can be downloaded here
http://www.microsoft.com/downloads/details.aspx?FamilyID=8e6ac106-525d-45d0-84db-dccff3fae677&displaylang=en
Don't forget IETab for Firefox... making things that little bit easier. Though IIRC, you can only use this to test the version that's default on your system.