I might be off base here, but if your idea is good, you shouldn't need fancy animation with your presentation. Keep it really really simple, with white on black text, and let the idea shine through.
Simple PowerPoint can do this but beware that the animations and sound effects are very very hackneyed. For a fun take on this, see Peter Norvig here.
If you later decide that you do need to have a fancy presentation for marketing then hire an external agency to do it for you. It's surprising how inexpensive a proper professional sales video can be and how much better it is than a home-made alternative.
I use a combination of Apple Keynote and Omnigraffle. (both Mac-only) I find very simple graphics, with spare animation can tell a story very effectively.
I've also seen some folks do nice work with Prezi.
Too many of the "serious professional tools" are just unusable unless you spend a lot of time with them. They are very powerful for folks who make their living at it, but for the rest of us they are just too much.
For great examples of visual descriptions, as well as an excellent agency for creating these sorts of things, check out Xplane: http://www.xplane.com/ and Dave Grey's blog (He's the Xplane founder and chairman): http://communicationnation.blogspot.com/
+1 for Camtasia. If you want to look professional, you need to upgrade to pro-level tools. They have a free trial if you want to check it out.