I watched a family member a few years ago, spend an hour per week in speech therapy. He was young - 6 years old - but his language skills were developing properly. We all noticed that his speech was hard to understand. Once he was tested, his vocabulary (understood and spoken) turned out to be small.
In therapy, there was a long series of exercises with his mouth and tongue to build muscles and habits to improve his enunciation. There were alot of flash cards and exercises to build his vocabulary.
It was all very pricey and, since the problems went away, we were pleased with the results. I was struck at the time by how technology-void the therapy was.
I've just seen an article which points out that some of the free online word games provide the type of therapy that many families pay for. Take a look at the article on games for word retrieval therapy.