Kevin Wick has posted a very nice sketchy-styled Axure library.  I highly recommend it.
Prototyping in a very low-fidelity visual style generally helps your stakeholders provide feedback at the right level, as discussed in this article, and has been adopted by many other design tools, notably Balsamiq.

I recently joined a wave of about seven user experience professionals, with all of us participating and discussing, in real-time, the merits of Wave. In fairness, if you send seven UX snobs to review almost any interface, you can expect some berating. And this is a closed “preview” (read: beta) version. But [...]