[catone]

I usually just use a text file (Textmate is my editor of choice) to create a spec sheet describing what my idea is and how it works. From there I share that planning doc with my partner and we start making mockups together (or more likely, she does, since my Photoshop skills suck). If I need to make a mockup for her to clarify something in the text file, I use Photoshop, or since my Photoshop skills suck, pen and paper (not that my pen and paper drawing skills are any better).

No wow factor, but it works for us.

To present ideas to people on the outside, I usually just do it verbally or via email. You should be able to explain your idea in relatively simple terms using nothing but words, imho. Again, no wow factor, but it works for us.