Here's a bunch of string tutorials I've found on various blogs. If you see one that could be linked here, email me with the link at strings[at]mts[dot]net.
Leigh's 12 inch String X block, which links to Bonnie Hunter's 14 inch String X block
LuAnn's Heart Strings Table mat
Cathy's Endless Chains quilt
Foundation-free Strippy Scrappy Flippy Happy Happy blocks by Teresa
Lynn's foundation-free strippy blocks (not diagonal)
Paulette's String Double Pinwheel quilt. click on the link to see pictures of the quilt, and then follow the multi-part tutorial linked in the sidebar
Paulette's string block inspired by a chocolate bar wrapper.
Ashley's foundation-free Scrappy Triangles quilt
Beth's basket weave string block
Michele's string block tutorial and links to other tutorials