Some of his most famous roles in video games are Teryn Loghain from Dragon Age: Origins, Gabriel Roman from Uncharted: Drake's Fortune and Peirithous from God of War III. He has also appeared in Mass Effect 2, Knights of the Old Republic and Lord of the Rings: Conquest.
Possibly his most famous role is as the vampire Kain in the Legacy of Kain series. This is where I first heard Templeman's voice, and it was awesome. He's got quite a regal tone to his voice, one that has a subtle command of power. If you haven't heard his work then I strongly suggest you YouTube him.
Can you think of any distinct voices in the genres that you think fit perfectly? Here's a video of Templeman and the late Tony Jay (another amazing voice actor) doing outtakes for one of the Legacy of Kain games.