I never was able to get Afloat to work for anything. I know WindowShades by Unsanity can do it, or could back in the day (Does it still work) but it's an APE and a lot of people have issues against them. I used it a lot. But haven't in forever so I just lost interest in ever needing anything on top except Movist which does it by itself.
Edit: Oh, hey. I just discovered this new Snow Leopard only setting for Dock Stacks called "New List View". In normal "list" view, you get a normal menu of icons, but the new list view is like a hybrid of grid style (Where you can dig down) and list view. Instead of cascading menus, it's a folder set to list view.
You can enable it by using the awesome "Secrets" preference panel. DOWNLOAD IT NOW!
http://secrets.blacktree.com/
Which brings up an annoyance I hate about Stacks, the "Open in Finder" icon is always at the bottom of the list. Why can't it be at the top? So you can click it to open the folder without having to scroll? Makes no sense. The perfect position for it would be top right, you know, like how the back button is top left, just put that icon top right, Apple! Would make a hell of a lot more sense.
* And if you're wondering about my stack view, I made the new graphics myself. Got rid of that ugly white border and made them recessed. Same with my Dock.