The best suggestion I could give you wouldn't be necessarily a Mac app, but its a cloud CRM written in HTML5 and CSS 3, so it's accessible from any browser and they have native mobile and desktop apps coming soon.
It's JobNimbus. By far the easiest CRM software to use, which is something you really have to look for. Everyone CRM says they're easy to use, but the industry in general just drowns in bad adoption rate (see here) because of the terrible software they make, so you have to get in and try it out.
JobNimbus has a free 30-day trial of their Pro version, but you can still use it after that as a Basic version with less features. It's also not just CRM, but also project management, so it makes it even easier to streamline your workflow.
Go ahead and check it out, maybe try it for a couple days and see what you think: http://www.jobnimbus.com. Their customer service rocks too. I'm using it and can tell you, you won't be disappointed.