Depends on whether your willing to pay or not and what your os is.
Virtualization usually gives you the breadth of choice of browsers, so services like http://www.browserstack.com and http://www.spoon.net (spoon offers a free service for personal use).
Next step down is screenshot base services, like http://www.browsershots.org and http://www.netrenderer.com/
The draw back with screenshot services is usually there’s a queue time though the latter doesn’t but is dedicated to IE versions only, screenshots don’t lend themselves to well to debugging I find but they can serve a purpose for side by side comparisons.
You can always your own virtual machine with various versions of IE on though there is time and effort involved in getting it running plus needing a copy of windows. But if your on windows already microsoft has actually prebuilt virtual machines for this task that your can download at http://www.microsoft.com/en-us/download/details.aspx?id=11575
read the install licence’s carefully though.