You say "Manyatta," I Say "Rip-Off"
Although you'll frequently be hearing about opportunities to visit a Maasai manyatta, it's worth knowing that this name is a bit of a cultural misnomer. Maasai villages are not, in fact, called manyattas, but are actually enkangs. A manyatta -- or i-manyat -- is something quite different, in that it's a place of temporary encampment established specifically for warriors (morani) to live during the eunoto period, during which they pass into elderhood. The manyatta may comprise about 50 huts, and all the members of one age group in a district live there. Living together as they learn about the new social hierarchy into which they've entered, these men are taught their responsibilities as future husbands and tribal leaders. The enkang is a semi-permanent settlement (although it may exist in one place for many years) and consists of 10 to 20 huts (which are built by the women) with several families who communally care for their livestock. The settlement is surrounded by a thorn fence, which serves both to keep cattle in and unwelcome visitors out.
There are also cultural villages -- also known as fake manyattas -- built exclusively as tourist attractions and staffed by Maasai who dress up purely as spectacle (and for your photos, of course), as well as enkangs that have become so commercialized that they might just as well be billed as Maasai souvenir stalls; costs to visit these places run anywhere from $10 to $40, with much of this being pocketed by unscrupulous guides, drivers, and tour operators. And then you'll spend much of your visit being cajoled into purchasing handicrafts at criminally inflated prices -- the experience is unpleasant, at best.
If you would like to visit an authentic Maasai enkang, talk with the manager of your camp or lodge about the kind of experience you'd prefer, and insist on being accompanied by a Maasai guide who can not only explain the rhythms and complexities of the daily life of the people you are visiting, but also act as a translator so you can engage your hosts in meaningful conversation. Once there, crouching down inside the dark, smoky interior of a dung-smeared Maasai hut or witnessing the poverty and relative filth (by Western standards, at least) and the simplicity of these people's lives, it's unlikely that you will not be moved. At some point, bags of handmade crafts will be hauled out; making a donation by buying something is a gracious way of thanking your hosts for an eye-opening interaction. And don't forget to honor any promises to mail any photographs taken of the people you meet.