The Lux TX500U is my favorite all-around option for an affordable programmable thermostat, one that I would highly recommend. Available for $30 on Amazon, Home Depot and elsewhere, the TX500U is slightly pricier than the other basic models I've tested. But this one is worth the extra 5 bucks.
Its main display features up and down arrow buttons and a hold button, with everything else tucked behind a plastic covering that folds down with ease. The covering is pretty flimsy, and it popped off once when I wanted to make some adjustments t0 the program settings.
It does keep the thermostat looking pleasantly minimal, though.
The TX500U also features a Next button. This may not seem like a big deal, but it made it much easier to figure out how to create programs. Most of the models I've tested in this price range double up on buttons so that a Program button also acts as a Next button. Not so with the TX500U.