I spent a couple of hours yesterday trying to make sense of all the new Windows 7 products. When I started we had 18 different Windows 7 products listed on the site. Half of them were Microsoft's N versions, these are the same price but with Media Player removed. Apparently Microsoft have to produce this version due to a European Commission fine back when XP was launched.
So I've removed the N versions. I then went on to divide up the other options into three categories. The full version for clean installs, the upgrade version for when you already have older Windows and the anytime upgrade for upgrading from one version of Windows 7 to another.
Within all these categories you get to choose from Home Premium, Professional and Ultimate versions.
Here's a few links you may find helpful when choosing which version is right for you:
MoreComputers Windows 7 page
PC Pro's everything you need to know about Windows 7 pages
Cnet's Crave blog about Windows 7 N versions page
I would post some links to the Microsoft site but I can't get on it today - must be a busy day for them. Will update this post when I can get access to their site.