I just finished Galileo's Dream by Kim Stanley Robinson.

Galileo's Dream covers Galileo's life from when he first started building telescopes up to his death.  The twist is that his first telescope is a gift from a mysterious stranger, who turns out to be a time traveler interested in using Galileo in a few schemes of his own.  Galileo gets entangled in these schemes, effecting his life and possibly all of the future.

An enjoyable book.  The point of view is a little strange.  At times, it is made clear that the story is being told by someone who is observing Galileo, at other times the narrative enters Galileo's head in a way that makes him seem to be the narrating character.