Glorious Papers (Techniques for applying colour to paper): Ruth Issett (Batsford) Ruth is a real colourist, and the ideas she has for using paint, paper and other supplies you can get from any artists shop are amazing. There's also a chapter on what you can do with the papers once you've made them.
ArtEffects: Jean Drysdale-Green (Watson Guptill) This book's for artists, but covers all sorts of media (inks, watercolour, acrylics, oils, pastels etc) and shows you how to use them in weird and wonderful ways to get great backgrounds.
Origami: The Art of Paper-Folding #1: Robert Harbin (1968, Coronet) It's as old as I am, good easy to follow introduction that gets quite complicated towards the end
The Origami Bible: A Practical Guide to the Art of Paper Folding: Nick Robinson (2004, Collins & Brown/ Crysallis Books) Again, a good solid easy to follow introduction that gets very very complicated towards the end. Bought this as I'm a huge fan of the Wet Folding or 'new experimental' origami section at the end. Not that I've ever tried it, I just look at the pictures.
On Paper: New Paper Art: Jane Thomas & Paul Jackson (2001 Crafts Council/ Merrell) Catalogue for an exhibition I never saw - the sections on 'new folding' and 'cut & constructed' are particularly inspiring
Fabric Painting for Embroidery: Valerie Campbell-Harding (Batsford) Valerie's ideas can be used equally well for paper, she has great suggestions for printing motifs using household objects (like half a cauliflower floret) and the illustrations are gorgeous.
Finding Your Own Visual Language (A Practical Guide to Design & Composition): Jane Dunnewold, Claire Benn & Leslie Morgan (Committed to Cloth)