Lifehacker suggests moving your documents folder, a download folder, etc. into the dock. Then right click that folder (or Control-click or simply click and hold...whichever you prefer) to see that folder's contents.
That's fine, but if you want to get fancy, create a smart folder to live in your dock. I made one to mimic Steve's collection of recent images:
- From the Finder's "File" menu, select "New Smart Folder"
- Set the criteria to be "Created = Today" and "Kind = Images"
- Give your folder a descriptive name (like "Today's Images"), save it and drag it into the dock!
Yes, this only the most modest approximation of the most superficial functionality of stacks, but it's the best we have until October.