First thing that popped into my head:
C5 Corvette. It is a ridiculously good performance bargain. The LSx engines are very reliable, parts are a dime a dozen and plentiful, huge owner community, rich aftermarket, they're fun to drive, you can actually fit things in them, and -- despite being a V8 -- you can get 30+ MPG on the highway with them. All of them except for the FRC/Z06s have the targa roof (or a convertible top), making it a superb summer car option.
And if it does need repairs? It's a Chevrolet, every mechanic you've ever met can probably work on them, and none of the tools or fasteners are proprietary. Want to upgrade the stereo? It's your standard issue double-DIN head-unit, buy whatever you want and a harness and trim kit and you're done. You can go from AC Delco tape deck to touchscreen navigation with bluetooth streaming in an afternoon if you want. There is no "I have to get down to the dealer so they can code this thing" when you buy a battery or install something aftermarket. My dad picked up his dream car (a 2001 C5 6MT Targa) and he loves it. If he needs to do anything to it, he can.
Other things I'd consider, S2000 was already mentioned as was the newer Miata. I would say older Porsche Boxster except for the lack of access to the engine giving future repairs and maintenance the potential to cost a lot of money in labour, but those cars handle like a dream and aside from the IMS bearing issues in some cars which has mostly been resolved by now (get proof), Porsche is known for being a very reliable marque.