Then I stumbled upon a neat feature in OS X that will announce the time every hour, half hour, or quarter hour. To enable it, go into System Preferences, then Date & Time. Select the Announce the time check box and the desired interval.
You can also change the voice for the time announcement by clicking on the Customize Voice button.
Though this solution isn't perfect it seems to be working well for me. The only catch is that in noisy environments or when I have the audio off I can't hear the notification.