Ideas on small towns to chill in

You may want to consider Filandia, Quindío. It's a beautiful small town in the coffee region, relatively close to Salento and the Cocora Valley. Despite its potential, it's still somewhat outside the tourist radar, and the people there are working hard to bring it closer, so there should be plenty of opportunities there.
safe travels!

This really might not be what you want, but we enjoyed our volunteering work with Angeles de Medellin, which is on the hillside in Medellin. You could base yourself in Medellin, which is a fun city and has the climate of eternal spring and visit the nearby towns on the weekends? From Guatape to Jardin ... Medellin living has some advice on the surroinding towns (as well as info on living in Medellin) http://medellinliving.com/?s=pueblos

I'd suggest Salento, or Villa de Leyva. The latter has hot springs nearby.
Salento has one touristy street but all the rest is nice and quiet with very friendly people. The hike in the Cocora valley is amazing.

I didn't like Filandia much...

You might want to consider Riohacha, La Guajira. Ok I must admit it is more eternal summer than spring but you have a beautiful ocean, you are close to the desert and the Sierra Nevada de Santa Marta. I could help you find an indigenous community to work with.

Villa de Levya, Barichara and Salento are probably too touristy for what you're looking for. They don't need anyone to teach English in those towns. Finlandia or Riohacha (if you like it hot) were good suggestions.

Also, maybe Buga in Valle de Cauca, north of Cali could be nice. Or the small city of Popayan further south has perfect weather. Or there are some really nice small towns south of Medellin, like Jerico, la Pintada, Santa Barbara, or Jardin. The last gets tourists, but nothing like Villa de levya.

Villa de Levya, Barichara and Salento are probably too touristy for what you're looking for. They don't need anyone to teach English in those towns. Finlandia or Riohacha (if you like it hot) were good suggestions.

Not that I know why 'touristy' would be bad for the OP, but you probably mean Filandia, not Finlandia. ;-) (Or Finland for that matter, haha)

Pamplona might be an interesting option for you.
It's situated at higher elevation thus the climate is moderate, spring-like. It's a university city with a sizable student community that might be a good base for you as English teacher.

Great ideas, folks. Gives me a lot of food for thought. Thank you.

In addition to what some of the other posters have said, Honda is an interesting town. It's in the Magdalena river valley, about for hours from Bogota. It's situated in between Bogota and the coffee region, and the town is full of interesting history. Before the advent of modern transportation (planes, trains, automobiles), the Magdalena river was the main conduit for goods coming down to coast to Bogota. Honda was the primary river port where things would be offloaded before they made the steep trek up to Bogota and the altiplano. The town has tons of architecture that can attest to its former status and if you visit, you're likely to be the only Gringo in town. The old part of the town is nicely preserved, and there's a lot of interesting history in the town and surrounding areas. The only downside is that Honda is very, very hot. If you don't like the heat, then stay away!