Check out the Chapala area. Up in the mountains, it gets mild, spring-like weather all year round. Also, it's the largest ex-pat community in Mexico, so you can get by with not too much Spanish. The only drawback is that it is more expensive than other places in Mexico (but still cheaper than the US). Ajijic is the main village where all the gringos live.
It's right beside a huge lake, very pretty place.