Not including anything from the company I co-founded: $10-$20 a month from publishing Hypersphere (a book written by the 4chan /lit/ board) which sells a few copies a month spread between Lulu and Amazon.

http://www.lulu.com/shop/anonymous/hypersphere/paperback/pro...

It was really fun self-publishing something and as an added bonus it's in the permanent collection of the MoMA Library.