I've been to Aranjuez, Avila, Alcala de Henares, Cuenca, Toledo, Segovia, Salamanca and Chinchon. I would definitely put Avila at the bottom of the list, and I feel no burning desire to return to Aranjuez--but I am not a palace person. Chinchon is a cute small town, but I 'd consider it a more minor destination than the remaining places. It requires taking a bus, and you'd almost certainly need to take the metro to reach the bus stop, at which point you'd need to figure out in which direction to walk a few blocks.
I'm pretty sure Salamanca is more than 2 hours from Madrid.
Edited to add: Nope. I was wrong. The train can take as little as 2 hr. 6 min. However, Salamanca has a large historic area, plus the university to explore. It might be a rather rushed day-trip.
Cuenca has a couple of nice modern-art museums. For art-lovers it should probably be quite high on the list. For other folks it's about the medieval district on the hill and the hanging houses along the ravine. Cost is an issue here; you really need to buy the AVE tickets early enough to get the promo fare, or the price will be somewhat painful.