Most pre 2001 Mercedes models with inline engines (room in the bay) are very easy to work on. I was able to do 99% of the maintenance and repairs on my 98 C230 with a small set of simple hand tools. Brakes, fluids, filters, belts, etc. all simple and easy to do.
Go back to the pre OBD-II era, and MB models are even more DIY friendly. As long as you stayed away from the complex models (like SL's or S-Class cars with tricky self-leveling suspensions, etc) those cars were simple to maintain and lasted forever.
But, if you want super-simple, look for North American iron, full frame or pony cars. Carbs, no electronics, leaf spring suspensions, etc. are dead simple and parts cheap.