If you find asteroids interesting (as I do), then here are a couple of great links for you:

Gerard Faure has an excellent " DESCRIPTION OF THE SYSTEM OF ASTEROIDS" (although it is a year out of date, and a lot happens in this field in a year.)

Petr Scheirich's page has some excellent graphical displays that try to show how these different "families" of asteroids are related. Be sure to check out his animation of the Hildas and Trojans at this link - it's probably the best visual explanation I've seen of what an orbital resonance is.

The Hildas especially are interesting - they're in a 3:2 resonance with Jupiter. All the other resonances with Jupiter (e.g. the 2:1 resonance) are empty. They're the "Kirkwood gaps". But the 3:2 resonance is packed with these "Hildas", the same way that the 2:3 resonance with Neptune is full of the Plutinos (including Pluto).

All orbital resonances are stable - that is, if an object is in resonance with a larger object, it tends to stay there - so why are certain ones full of objects, and other ones, in the middle of a swarm of asteroids, conspicuous as "Gaps"? Why would Jupiter's gravity herd asteroids into the 3:2 resonance, but clear them out of the other ones? When I came to understand the answer to that question, (and it's not that difficult), I came to appreciate some of the intricacies of orbital mechanics. I'd try to explain it here, but I already have a reputation for posts that are long and pedantic .

So Nereid, you mentioned the sharp outer edge of the Edgeworth-Kuiper belt. It is often explained as the farthest away that objects condensed out of the primordal cloud that formed the solar system. However, there is another interesting fact about that edge. It just happens to be exactly at the 2:1 resonance with Neptune.

So, maybe it's not an "edge", maybe it's a "gap". And if it exists for the same reason that the Kirkwood gaps exist, it's a real "hint" as well.

The Oort cloud, now, I'll leave that for another post <grin>.