"Caesar" by Christian Meier is regarded as one of the best biographies.

You can also check out Caesar's own writings for a first-hand account - Commentarii de Bello Gallico, for his exploits in Gaul, e.g.

If you'd like a historical-fictional approach instead, consider checking out Colleen McCullough's Masters of Rome series. Its quite interesting, and well written historical fiction in that she dovetails her work quite closely to the evidentiary record.