The best, the most complete (up to the 1960s or so) is "Rogues, Buffoons and Statesmen" by Gordon Newell. This is a seriously thick book that covers almost every moment of Olympia's history (from the state government and local perspective) from pioneer days to the 1960s. Of course its incomplete now because its so old now, but still very complete.
The second best book would of course be something that updates RB&S to the current day.
Here's what I wrote about it earlier:
Generally speaking, the books tells the story of Olympia from main street and the Capitol. Gordon was an old time newspaper guy in Olympia, so he had great background for both Olympia scenes. He also lived early enough in Olympia's history that the really old stuff really wasn't that old to him. It is oft-referred to, but seldom seen. There are only six copies in the Timberland system, a few of which don't circulate.
The lack of local library (or even digital editions) is made up by there being a lot of affordable copies online. Right now, Amazon has several copies under $20.
The second is "Confederacy of Ambition." Certainly less of a total history than RB&S, but also deeper (if that's possible). My earlier review.
This book is great because it takes on the glossiness that people put on local history when they're being lazy. Like this:
Washington began as a state founded by optimistic settlers with utopian dreams, and to some degree that sentiment continues resonating.
Uh, no. If William Winlock Miller was the typical settler (and I think he was), he may have been optimistic, but he certainly wasn't utopian. He was a driven, realistic, politically savvy and business focused sort of guy.
Or, more simply, it fills in with personal history the gaps that are left when you do a local history that just names names and takes down dates.