The Osprey Essential History series has been released digitally at 99p a title. These were rather high level overviews and dubious value when they were full price but I think at this cost could be worth a look as an intro to a period. They're on the kindle store too
http://www.ospreypublishing.com/guide_to/ (http://www.ospreypublishing.com/guide_to/)
Thanks, 2 bought, agree good price.