I recently ran across this brain training game website that is… free! And it has all of the basic features every paid for service I’ve used has (including “brainbuilder” and “lumosity).
Some of the included games are notably ones used in scientific studies for measures of working memory, etc. These included: auditory and textual digit span testing, forward and backwards, stroop, and dual n-back tasks.
Check it out at http://www.cognitivefun.net
And big props to the guys that put this together.