Cross-stitch is a very common technique, used formany different design. There are many variations, with the most common technique today being a simple "x" over 1 or 2 threads in the fabric for linen/evenweave, or over fixed blocks in Aida fabric. I have made most of these things from various kits or from patterns in books - my favourite designs are by Teresa Wentzler. My favourite books for cross-stitch patterns are:

Elizabethan Cross-Stitch by Barbara Hammet

Celtic Cross-Stitch by Anne Orr and Leslie Clarke

Celtic Cross Stitch Designs by Carol Phillipson

Celtic Art in Cross-Stitch by Barbara Hammet