[HappyCatMachine]

iMockups for simple wireframes that are quick to build and easy to understand for the wireframe layman client.

OmniGraffle for more flexibility but with a tradeoff in how much time it takes to build one.

Sketchpad for hi-def wireframes but only if I feel the urge when on the train. Usually I'm at my desk with Illustrator by this point.

I do use papers, it is excellent actually. I usually leave it out of reviews given that it only applies to those in the academic community but yes, it does the job very well as long as it's papers one is reading. For larger PDFs GoodReader excels.

Sorry for terseness, I'm a wee bit busy but glad to see a reply.

Cheers