I recently came across a site called the Transformation Archive. They have a couple hundred stories on transformation. Ranging from mythical beasts, to the other sex (most men changing into women, they are quite detailed if you know what I mean).
Here's a story for anyone who is interested. It's about this 25 y/o man, who accidentally gets transformed into his Co-Worker's 17 y/o busty niece, through DNA transfusion.