After importing pictures into Aperture how can I find them in Finder? When I import pictures from my camera using Aperture I can find them by using Aperture to browse through its library, but I generally want to access them from Finder.

Where might they be?
If you right-click on the package used as Aperture Library, and select "Show Package Contents," Finder will show you the directories contained in the package; inside "Masters" you will find the pictures.
In my case, they are contained in a subdirectory of "Masters."