A new site on economic history gives links to two online books on economic history:
The first one by Gregory Clark A Passage to Alms seems readable to non-experts like me.
The second one is by Brad DeLong Slouching Towards Utopia: The Economic History of the Twentieth Century.
Tyler Cowen describes Clark's book here
Rajeev Ramachandran commentson Clark's book in two posts in his blog:
Abi at Nanopolitan points to this interesting Mark Thoma's commentary.