William Horton recently published a book called "The Icon Book" (Wiley, 1994) with practical advice on icon design. The book includes a disk with over 500 icons for common functions. Some companies have done icon testing to establish the strength of relationship between an icon and software functions, but most of that is not published. There is another issue you might consider -- the context of a set of icons may affect their identifiability. For example, when you put icons together in an icon bar, a particular icon's identifiability is affected by the surrounding icons. At my company we tested some icons individually and they were reasonably identifiable without a label. When we put them in an icon bar, a few were too similar to adjacent icons and we had to make some changes.
The research strongly supports putting a label with icons to make learning quicker. Of course, a label can create problems for international products (unless you create separate icons for each international product). Some Windows products are putting up a time delayed label for tool bar icons. The label appears after about 2 seconds and then stays up so you can scan icons on the toolbar.