My neighbor has a great analogy for this. It's about groceries, but applies to everything. If you go into a store for just 1 item, you might get it. If you want to get 2 or 3 items, you will get them but tend to forget the original item. And if you have a long list of items, forget it.
Asking like this, you will probably get so many different answers it will be impossible to make a decision. It's also hard to recommend anything because the different cameras and systems really are different, and you don't know much until things are in your hand. The Pentax line has some small cameras, the MV I'm selling (shameless plug) is tiny, and takes a lot of different K and M42 lenses, so that system is hard to ignore, especially at their low prices. Pentax has some interesting MF and AF cameras.