There are forty icons (well, one is the default, so that's 39 actually) for you to play with. The icons themselves are from the "silk icon set" from Mark James.
I replaced the regular book/page icons also with nicer-looking true color icons from the silk icon set.
So, as usual, do let me know your thoughts. Oh, and the set of icons will be fixed (at least for now), so if there are any suggestions for new icons, do let me know before v2.0!