I came across this blog post of op art fabric square letters that could be bought and used to make cushions ..quilts etc unfortunately the post is from 2008 and the shop no longer seems to stock them..I say bring them back! (found via balladora)
I don't think its possible to do a post on Op art typography without mentioning the legend that is Lance Wyman..but on second thoughts he deserves a post of his own..coming shortly!