Mockingbird : Mockingbird is an online tool that makes it easy for you to create, link together, preview, and share mockups of your website or application.
iPlotz : Wireframing, mockups and prototyping for websites and applications
Origami Studio : Origami is a free tool for designing modern user interfaces.
BLOKK font gives you a nice fill text for mock-ups and wireframing without the lorem ipsum. The new and better wireframing font.