I love the ABC Tumbling Blocks by Marci Baker. It's how to make tumbling blocks WITHOUT y-seams (
http://www.amazon.com/ABC-3-D-Tumbli.../dp/0965143961).
Also her Oh My Stars. Same idea, no y-seams (
http://www.amazon.com/Marci-Bakers-O...d_bxgy_b_img_b)
And Boo Davis' It's Okay to be Square. She's made very cool designs without triangles/diamonds/etc (
http://www.amazon.com/Dare-Square-Qu...9259540&sr=1-1)
Amazon links since they're easy to find, not because I'm telling you to buy them ;)