I actually just sketch out all the elements using pencil and paper, then resort to Photoshop/Illustrator to create the wireframes/mockups. I end up spending about 20-25% of my total time designing on my Mac.
With that said, I've found some useful tools for making mockups, quick and dirty:
Flinto - for quick prototyping, animation testing, and UX flow
Indigo Studio - wireframing and UX flow
Briefs - mockup, wireframing, and UX flow