2Remember offers a reminder alternative to OS X's built-in options

You can easily set a reminder on your Mac with the Calendar app. An alternative is 2Remember from Tropical Software. 

Why use 2Remember instead of one of the "built-in" Mac OS X apps. You may not need to. Or you may find Tropical Software's $9.99 app simple and uncluttered enough to prefer it.

The Tropical Software utility only takes up a tiny (semi-transparent) space on your screen, but offers various options for to-do's, including flashing icon on dock, flashing tab red, alert and sound. It hides just off-screen as soon as any other app opens, but reappears when you move your mouse over the tab.

One gotcha: if you use Mission Control to switch to different spaces, you have to remember which "space" has the tab, which is a bit inconvenient. The good thing about 2Remember is that you can download a demo to see if it meets your need better than Apple's default apps. 

The Tropical Software tool requires Mac OS X 10.6 or later. It's available at the Mac App Store, as well as the Tropical Software website.