I just found an interesting SEO ROI Calculator tool from SEER Interactive. Since I'm still in non-work mode and have only a few minutes at a time to be online, I don't have time to really test it out. However, it looks really cool, and if it works well, then it would be sweeet.
It includes the following form fields (and uses cool sliders to make adjustments):
Search Volume per Month
Click Through Rate
Lead to Sale Ratio
Each one has a little question mark icon that you can hover over to get the help tip for that item.
If you try it, let me know how well it works. I can't wait to be able to spend some real, quality time doing some SEO work again. I miss it. 🙁