[OT maybe?] X Window programming guides / books?

[pk]

Hi!

I'm a newbie when it comes to programming applications for X. Therefore 
I would like to purchase a good book to learn a bit more. However I do 
not wish to tie myself to any particular toolkit (like Motif, GTK etc.), 
yet. Does anyone know any good books available (most I've seen on XLib 
are out of print)? Furthermore, are there any resources available to 
convert applications from XLib to XCB?

Best regards

Peter Karlsson