🚀 go-pugleaf

Try the following 2 books.  Both just deal w/ X (only touching upon the toolkit
and Motif):

  "X Window Applications Programming"
  "Advanced X Window Applications Programming"

  (both are written by Johnson & Reichard and are printed by MIS:Press
   and cost about $30)

For the X toolkit (and a little motif):
  "The X Window System Programming and Applications with Xt (OSF/MOTIF Edition)"
   (written by Douglas A. Young, published by Prentice Hall)

For Motif:
  From the O'Reily Series, the one on Motif programming (I don't remember the
  exact title, but I've seen it, and it looks great).

Hope this helps,
Chuck Hines