I know a lot of people are either using screenshots or an actual mac with os x as a reference when they make themes, but I found some very, very useful information on the osx interface.
The link above shows the finder menu, and the edit, view, window, help etc. menus can be seen in the links on the left.
Also, the whole documentation can be downloaded here: Inside Mac OS X: Aqua Human Interface Guidelines (PDF)
Use the links on the left side to go to different aspects of the ui, a lot of them have pictures and actually explain pixel sizes for elements and stuff.
Also, here is the list of all the screenshots used in that guide.
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