1. Wikipedia's History of Buddhism
The History of Buddhism spans the 6th century BCE to the present, starting with the birth of the Buddha Siddhartha Gautama.
2. HistoryWorld History of Buddhism
An abridged version for those who don't have much time to read.
3. History of Buddhism for Kids
Simple resource and easy reading for the young readers.
4. Zen History
A brief, but decent history on Zen.
5. Religion of the Samurai
A very thorough resource (an entire book) on Zen in relationship to the Samurai, including a very comprehensive history in the first 2 chapters.