Since Erin posted one, I thought I'd post a couple of links to web comics that have TG elements. The Wotch (sic) has two main male characters who regularly get changed to girls, and several other TG elements (Including one male highschool teacher who was changed to a japanese school girl, complete with sailor fuku, and has been stuck like that since then.)

Minimal erotic content, so don't go looking for anything past a PG rating