Logoist 2 (introductory price of US$14.99 on the Mac App Store) is a terrific logo creation program that can help you turn out professional looking logos for stationary, presentations, invitations, postcards, just about anything where you need something artful.
I took a look at the original version more than two years ago, and the new version is completely rewritten and far more powerful.
Object groups and style groups
Flexible boolean operations (even multiple) for all paths (Path A + Path B - Path C = Path D)
Completely redeveloped user interface
Vector PDF export
Combine pixel and vector based effects
Smart Presets: Pre-Configured presets for christmas cards, birthday cards, logos, photo collages...
Many new filters and effects
Better path editing tools
Smart align and distribute tools
X-ray mode to quickly inspect projects
Thousands of cliparts added
Many new preset styles
I created some simple logos from the included templates while testing the app today. That's just a matter of replacing the sample text, moving some elements around, tweaking colors and modifying where shadows fall. It's also pretty easy to create something from scratch, and there are complete instructions built into the app, but if you are like me you'll start out with the templates. The app supports output as vector graphics or to Photoshop, and contains enough decent looking clip art to keep you from searching all over for what you need.
I'm impressed with the speed and flexibility of the app. Not everyone will want or need the power Logoist 2 contains, but for this very low introductory price you may find you use it more than you think. You can view a video of the app in operation at the developer website.
Logoist 2 requires OS X 10.9 or later and a 64-bit processor. It's ready for Yosemite, and it worked fine on the current beta of the upcoming OS.