One of the things you really need to remember when developing a custom CQ5 component is that regardless of what it is, what it does, or what it smells like, it must have a child dialog component for it to be available in the sidekick for Authors to use. Even if it does not need a dialog to accept any user input, without the dialog the component can never be chosen from the sidekick. So if you’ve created a component and cannot find it in the sidekick, this may be the reason why.

Moral of the story: One Dialog to rule them all…