Apologies if this is in the wrong place or is a duplication of an existing topic

Could anyone recommend books/DVDs for a poker fanatic that are slightly out of the mainstream?
Hilger, Sklansky, Harrington etc are known about, but there might be a little gem out there which is not so well known.
The intended recipient plays low stakes limit hold'em mainly but is as far as I'm aware profitable. He also plays low buy in MTTs & S&Gs.
It would be great if any suggestions were available to purchase on-line

Thank you in advance for any help - much appreciated.