Ah, yes. A subject I have debated internally and with others for quite some time now. I agree with the "RWD is better" sentiment, though I wouldn't completely rule out FWD, some of them handle quite nicely, and if the right deal were to come along, I wouldn't turn it down. That said:
E30: Still seems like the best choice when you factor in coolness. RWD with a reasonably powerful and torquey engine, decent suspension layout, huge aftermarket, tons of online support, and a spec racing series to provide knowledge and spares. Small enough that you can run it on 15" wheels for nice, cheap tires. Light enough that it won't eat those tires (and brake pads) for lunch.
E36: Probably the most logical choice. They seem to be pretty easy to find, especially the earlier OBD1 cars, for cheap. Cheaper than E30s, and they have better brakes, more power, better rear suspension, and many other advantages. Disadvantages would be that they look like 90s bland-mobiles (and yes, I include my M3), and they are heavier than E30s.
Miata: It is a good choice, though I have to agree with you on them. They just don't do it for me. I had one, I don't see myself ever going back. The problem with tracking one is that you absolutely have to have a bar, which immediately creates compromises in a car with such a small passenger area to begin with. IMO, convertibles don't make good track cars. I'd rather have an actual roof over my head.
924/944: Great looks, good suspension, very proven, can be found for reasonable money if you look. The issue here, as others have said, is the cost of keeping it running. Some consumables aren't too bad, but some of them will make your jaw drop.
Escort ZX2: Probably not a bad idea, though I don't know how the aftermarket is. You might even be able to score an early Focus for this kind of money, which is a very fun car with lots of aftermarket support and bolt-on SVT parts. My only concern there would be that it seems like it would be kind of top-heavy for track work. That, and the availability of LSDs.
Civic: I honestly don't know much about them except that Honda builds good stuff and the aftermarket is huge.