Autodesk DWF Viewer
Full user review
"Great product, but has bugs"
This is a great plug in for IE to view DWF's. It's been very handy to have.
There are problems with Autodesk when you use it with IE6. I uploaded to IE7, then it took almost 5 minutes to prompt me to load when trying to view a drawing. Once it did download thow, it worked great.
It really is a great plug in. I like the newer version that gives me the ability to mark up a drawing and save it as a different file. It's kind of like having full Adobe, but it's free.