If you ever struggle to find your Mac’s cursor then I recommend that you use MouseLocator. This free application puts a halo around the cursor to help your eyes locate it. You can configure how long the halo is displayed. It can be displayed for as little as half of a second, permanently or somewhere in between. You can also control how long the cursor must be idle before the halo will re-appear.
I find that MouseLocator is popular with people who use very large monitors or whose eyes are tired. I do a lot of computer-based presentations and I consider MouseLocator to be an indispensable tool. When I’m projecting my laptop’s display onto a large wall, MouseLocator helps audience locate and track the cursor as I move it around the computer screen.
Check out MouseLocator.
[Update: December 2015. OS X El Capitan (aka OS X 10.11), which was introduced in September 2015 adds a new feature which helps you locate your cursor. You can simply wiggle your mouse back and forth, or, if you have a trackpad wiggle your finger back and forth on the trackpad. After about 2 seconds of wiggling you should notice that the Mac’s cursor temporarily gets larger. This allows your eyes to locate the cursor more easily. If you don’t like this feature you can follow these instructions from OS X Daily to disable this feature.