I'm about 3/4 through The Years of Rice and Salt by Kim Stanley Robinson.
It's an incredibly ambitious alternate history about how the world would shake out if a plague killed 90% of Europe in the 14th century. Each section is a novela about a set of characters in a different time.
He's probably my favorite living author; he normally writes sci-fi, occasionally dips into historical fiction (or a mix of the two genres), but always meticulously researches his subjects in a way that brings his worlds to vibrent life.