More to explore:
My favourite method for joining squares from Carina's craft blog
CROCHET granny square joining tutorial
Granny Square Joining Tutorial. Genius. Love the way it looks! Blanket I made using this joining method: http://www.ravelry.com/projects/kninerts/granny-square-pink-purple-and-white
joining granny squares with granny stitch! - tutorial
Oooo... I like this... Granny square joining tutorial that looks like an extra row of stitches.