Dual n-back, mentioned in the post just above, is a simple working memory game of unbounded difficulty. A version of the game is available to download free of charge from this site for example: http://brainworkshop.sourceforge.net/
One problem with working memory training games is that, while the effects on the brain from regular play are truly impressive, the games require a lot of self-discipline to play regularly. They are quite boring to play almost every day in the long term, even for an individual with an Autism Spectrum Disorder, who may thrive on routine.
Cogmed, an evidence-based intervention for improving working memory and attention, attempts to remedy this problem. Cogmed offers close professional support in addition to ensure maximum compliance with the training…
In addition, the Cogmed system has plenty of research behind it supporting its use. Cogmed’s founder and Chief Scientific Officer is Dr. Torkel Klingberg, a well respected and experienced researcher in the field. For an example of the research behind Cogmed, below is an abstract of a study utilising the system for kids with Autism Spectrum Disorders…
(sources: http://www.cogmed.com/how-is-cogmed-different#.T6ehJHorzKR; http://www.cogmed.com/retrospective-chart-analysis-follow-cogmed-working-memory-training-children-autistic-spectrum#.T6ednnorzKQ)