Language model describes possible word sequencies. A good introduction to the language modelling things and challenges beside the conventional literature are the following surveys:

Two decades of statistical language modeling: Where do we go from here by Ronald Rosenfeld

A Bit of Progress in Language Modeling (2001) by Joshua T. Goodman

A lastest trend is discriminative language models and recurrent neural-network language models

They demonstrate a good performance and a lot of interest is devoted to them.