Like it or not, Apple's iPad has transformed computing, mobile and otherwise. Introduced in April, 2010, it was the first tablet to succeed as a mass-market device and it remains the category leader, in sales.

Research firm Gartner predicts that that Apple's iPad will account for 73.4% of worldwide tablet sales in 2011, down from 83% in 2010. A wave of Android-based tablets has been challenging the dominance of the iPad. Early mover advantage aside, the iPad is a unique device and if you own one, or are considering buying one, you owe it to yourself to find the truly epic, must-have iPad apps.

There are about 140,000 apps written specifically for the iPad, which will also run most of the more than 500,000 apps in the iTunes App Store that were written for the iPhone. There's no shortage of worthwhile apps, but the best ones can be hard to find.

What makes an epic app? Well, there are many different ways to define greatness. Like beauty, greatness is in the eye of the beholder. So we've chosen to focus on some epic apps instead--the ones you simply must have, day-to-day for productivity reasons, and the ones that you will enjoy the most.

You may well ask whether there's any difference between great apps and epic apps. And you'd be right to do so. But rather than engage in a pointless debate about semantics and standards, take a look through our gallery and let your world be rocked by these apps. Then, when you're done, feel free to rain on our hit parade in the comments section. You know you want to.