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.