I'd been looking for this for a while, and today my aunt sent it over as an email forward:
Olny srmat poelpe can raed tihs.
I cduoln't blveiee taht I cluod aulaclty uesdnatnrd waht I was rdanieg. The phaonmneal pweor of the hmuan mnid, aoccdrnig to a rseaercehr at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be in the rghit pclae. The rset can be a taotl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Amzanig huh? Yaeh, and I awlyas tghuhot slpeling was ipmorantt! if you can raed tihs psas it on.
(It turns out not to work for HTML. Also, you don't have to pass it on.)