The Wrath of Khan

Mongol, a Russian-directed Mongolian-language film about the early life of Genghis Khan that I saw Friday night is kinda weird but also kinda awesome. In the "weird" drawer, it's a very long movie and yet ends with the unification of Mongolia -- all the serious conquering is left for a sequel. But it's awesome enough that I'd definitely go see a sequel.

It also made me a bit interested in the actual history of the period. Are there books on the subject that people would recommend?