The main book is "Transmitter Hunting - Radio Direction Finding Simplified" by Joe Moell K0OV and
Tom Curlee WB6UZZ. Information is here:http://www.homingin.com/THRDFSinfo.html
This was published in the 1980's, and Joe has discussed various updates, but nothing has been
published yet. Joe wrote the "Homing-In" column in 73 magazine for many years, and it now
appears periodically in CQ-VHF. That was the main source of DF information published in the
US. You can find a list of his articles (and lots of other useful information) on his website athttp://www.HomingIn.com
The links page should lead you to lots of interesting reading.
If you are particularly interested in the on-foot version of the sport (often called ARDF), there
is (I think) an English book on the subject, and many web sites in Europe (and other places)
with projects, information, etc. Joe's website should have links for that, as well as reports and
photos from various competitions. There is a video available also. I have a copy of a JARL
video titled, "Let's Enjoy ARDF", which is fairly self-evident in spite of the Japanese text.
(I normally turn off the sound and add my own narration.)
Otherwise I have some introductory materials that I often use when I do club presentations
that might be helpful for you. Drop me an email and I'll see what I can do to help.