I've got Pole in my blood and especially with what's going down in Poland today I've been very interested in reading up on how the nation has changed over time.
A good English language source for the History of Poland is Norman Davies two volume book "God's Playground". Vol. 1 deals with the Origins of Poland, up to 1795. Vol. 2 deals with the history of Poland, since 1795.
Poland: A History by Adam Zamoyski. It's a good chronological history from the origins to modern times. As mentioned already, Norman Davies' History of Poland is also a good read.