I've spent a lot of money (mine and clients') on different tools, and I've settled on Keynote. It covers 95% of my needs and I don't have to manage yet another tool.

Being able to sit in a meeting wireframing on Keynote is wonderful. Factor in another $15 for the iPad app and I'm cooking with gas.

Meetings get super-focused quickly when the participants can immediately see output.

I usually upload it to Google Docs post-meeting for the remote participants.

Protip: Save your mockup files as themes so that you can get to them quickly and easily.

side note: good looking mockups are dangerous because many managers and stakeholders don't know the difference between mockup and real application. They think you're done.

cool -- you actually create your entire wireframe in keynote?