I've been a Mac user for about five years now, but I've never been a fan of the Apple Mighty Mouse. They claim to have "touch-sensitive technology" that detects right and left click, but anyone that has used one knows that right clicking can be a struggle. Sometimes you'll hit the sweet spot, but most often you will just give up and hold down the control key and click for the desired effect.
The first thing I always do when working on a new Mac is plug in my own mouse. Any mouse will do, but if you're looking for a really nice alternative to the Mighty Mouse that matches the rest of your Apple accessories, look no further than the Rocketfish Bluetooth Wireless Laser Mouse.
With its sleek white design and visible right/left click, you're getting form and function with this Mac compatible mouse. The scroll wheel also offers 4-way horizontal and vertical tilt just like the Mighty Mouse scroll ball, as well as a satisfying "click" when you scroll (albeit a bit loud, but that is a very minor complaint).
I picked this mouse up at Best Buy for $50.