[avenger123]

William Irvine's book - http://www.amazon.com/Guide-Good-Life-Ancient-Stoic-ebook/dp...

is a great summary of Seneca and Aristotle's stoic perspectives. It's not a long book and gives a nice overview of the highlights of stoicism.

[dangerlibrary]

Seneca's essays aren't terribly long, either.

http://www.amazon.com/Stoic-Philosophy-Seneca-Essays-Letters...