The biology of brain plasticity, including adult neurogenesis, synaptic plasticity, axon regrowth, and synaptic reorganization, is currently one of the most intensively studied areas of neuroscience. One of the burgeoning avenues of research for this field explores how altered plasticity may account for some of the behavioral and neural changes afflicting the aging brain, and is leading to efforts of fostering plasticity and thus "rejuvenate" the brain.
Perhaps the most popular products to emerge from this research are "brain games," which are activities designed to enhance cognitive function. These games have encountered a healthy bit of well-deserved skepticism from the scientific community; few of them have been validated by techniques even remotely "scientific" (by including, for example, controls), yet many make grand claims of improving some general notion of "intelligence" and well-being. There are, however, a few exceptions: "brain fitness" products emerging from within the scientific community, such as Posit Science, intended for people in their 60s and 70s, and Lumosity, which targets a younger population (i.e. baby boomers.) Since many functions, such as processing speed, working memory, and attention, begin declining around the age of 30, it seems reasonable to start on the early side.
Lumosity is a new program, so the games are still in "beta" phase and thus free, and these games are easily the most entertaining of any I've previously played (evoking behavior reminiscent of my childhood Tetris addiction.) More importantly, the games are inspired by research on human cognition; the company's head of neuroscience research studied with Jon Cohen at Princeton and John Gabrieli when the latter was at Stanford, among others, and there are a number of cognitive neuroscientists on the board of advisors. I recently met one of the founders at Stanford, and after discussing my research on adult hippocampal neurogenesis, I ended up joining these cognitive neuroscientists as a fellow scientific advisor. Anyways, the group at Lumos Labs performed a randomized, controlled study, which I can personally endorse, showing that Lumosity users improved on tasks of working memory and visual attention (there's an SFN poster and white paper available for your scrutiny as well).
Further scientific validation of the program's ability to improve various cognitive functions is certainly needed, and is in progress. Most importantly, of course, will be evidence that this sort of cognitive training can have long-term effects that translate to "real-world" functional improvements. In the meantime, the games are fun (with enticingly impressive high score lists) and certainly can't hurt.