The Balfour Declaration by Jonathan Schneer (Up to 1917)
One Palestine, Complete by Tom Segev (The British Mandate)
The Ethnic Cleansing of Palestine by Ilan Pappe (The aftermath of the 1948 War)
The Iron Wall by Avi Shlaim (Israel's Palestinian policies 1948-1998, possibly the best overview.)
The Israel-Palestine Conflict:100 Years of War by James Gelvin (All of the above).
Gaza in Crisis by Noam Chomsky/Ilan Pappe
The Punishment of Gaza by Gideon Levy
There's some recent 'beginner's guides' and 'basic introductions' which cover all the above and the historical period available too, which I haven't read. Perhaps I should!
Some of the above have been accused of bias (and one is particularly provocatively titled) but they're all good solid books with good reviews. My interest is mainly in the Palestinian side as I feel I've heard far less about that side growing up in Britain as I have done, but I'm sure someone will be along to recommend some others shortly.