It's hard to be specific without knowing what your skill set is. But if you are starting out, and would like to build up some understanding and competence in focal plane shutter mechanisms, then the early Praktica models are worth looking out for. They are very cheap; have a removable plate for their film gate, which makes reaching parts of the shutter system that are much more complicated to access on other SLRs very easy (watch for any shim placement under the plate, if any, for replacement in same location, though); and the speed escapement, which can be buried in the front of the body on some Japanese SLRs, is housed under the lower cover (along with the ratchets for the shutter springs) making access for cleaning this very easy. Contrary to what many people think about Prakticas, the best part is that, after cleaning and lubrication, and perhaps some minor adjustments to spring tension, it is not at all unusual for them to run very well again, meaning you should also have another usable camera.
If you are more interested in leaf shutters I'd suggest looking at something like an old Prontor first, a decent quality shutter that is not as complex as a Synchro Compur. I'd suggest staying away from the leaf shutter SLRs like Contaflex and Bessamatic to begin with. Personally, I like these designs a lot and don't mind working on them, but their additional complexity makes them not the best choice for less experienced repairers. Some of the classic Japanese rangefinders aren't too bad to work on either, although a few do have quite specific issues one needs to be mindful of (Eg some of the Yashicas). The Konica Auto S2 isn't a bad one to do a shutter and lens clean of, and the Hexanon lens fitted to it is a beauty. No real traps in it other than being gentle with the meter wiring and possibly a need to detach and re-solder it after repair.
There are a few books out there. The Tomosy series isn't perfect but it does have a lot of good basic information about how cameras work as well as tips for many of the more common models. I can't say I endorse his preference for lubricating cameras with graphite and there is the odd technical error in his comments about various cameras but they will get you started.
Cheers
Brett