Limiting goof off time...

Why?
If you use Firefox, like I do, there are extensions created to help you eliminate fun non-productive time. Here are a few examples:
MeeTimer - MeeTimer logs where you spend your time online, grouping it into activities, and actively discouraging time wasting.
I have it running right now. Although it isn't really set up to group or annoy me, I am in no way discouraged to surf the internet.
LeechBlock - LeechBlock is a simple productivity tool designed to block those time-wasting sites that can suck the life out of your working day. All you need to do is specify which sites to block and when to block them.
This assumes your corporate firewall doesn't already block them.
TimeTracker - Do you spend too much time on Firefox? Do you open tabs faster than you can close them? Cannot get things done? Keep track of how much you browse with TimeTracker.
I think all of these look at the glass as half empty.

Here's an online gimmick:
Timer - a browser-based egg timer. Counts down however many minutes YOU choose. Displays the running time in the browser title bar (or tab).

Why should I limit my non-productive time? Non-work time is fun time! Instead, try to be more productive so you can have more time to fool around.
Some positive productivity extensions for firefox:
Life-hack productivity extensions
Life-hack GreaseMonkey scripts - between the two lists, this one is better...

Previously mentioned by Zach, Todoist, which I have started using and paying for, really does help. Simple, yet efficient.
Another tool mentioned by Zach, which has a Firefox extension, Getting Things Done.

There are many tools, add-ons, and what not out there to make yourself a better cubicle worker (Lifehack.org, Lifehacker.com)...why not take advantage so you can be less of a cubicle worker?

So you can do stuff like this: