Someone asked Make a similar question (that was not Mac-specific). Their answer suggests Fritzing, too, and there are other tools mentioned in the post and in the comments.

I use Omnigraffle for drawing the simple circuits I use in my Arduino classes. For circuit design, I use Eagle. It's a "real" schematic capture program (i.e. CAD program for circuits) that you can also use to produce circuit boards.

Omnigraffle is great for producing really nice looking schematics, as long as they are not too complex, because it doesn't have the intelligence that a real schematic capture program does on how to maintain connection between components. Omnigraffle also doesn't have very many components in its library so you have to make your own for even simple things. Eagle's part library is so big it's daunting.

I recommend Eagle from Cadsoft. It's the best free schematic/layout editor there is in my opinion.

There is always XCircuit and MacSpice. They maybe overkill for whatever your needs are, but might as well learn from them too.

http://opencircuitdesign.com/xcircuit/

Limited on my hyperlinks, so... macspice dot com

Cheers,

Scott

You may be able to access some of the Linux stuff which is around, through things like MacPorts.

There is also OSX version of Eagle Cad. Although software itself is not very Mac-like nor exactly easy to use.

For drawing circuits I use Omnigraffle and the Electronics Extra.

For physical hardware diagrams I use Fritzing.

Checkout a video on Fritzing here.

Cheers,

Marcus