IEPlus is a browser plug-in for Internet Explorer that gives IE a lot of nice functionality enjoyed by other browsers like Firefox. My personal favorite is that it can restore a crashed session. That way, if IE dies when you have several tabs open and you end up having to kill IE, when you start it again it will give you the option to restore your session opening all of the tabs that were lost.

IEPlus also has features to improve tabbed browsing, and make quicker searches. It works on Vista and XP, and it supports IE7 and IE6. And it's free.