Here is the list of must-have paid apps that i've personally tested and after hundreds of hours of peeling through app reviews and testing, i've shrunk the list to the bare essential apps that you would be wise to spend on. Some of you might not agree with paying for apps, since there's such a huge collection of free or ad-supported versions. But in my honest opinion, these apps are well worth the price and will make you enjoy and appreciate the usefulness and power of your iPad.
1. AVPlayerHD $2.99
"AVPlayerHD is officially support for AC-3, E-AC3, TrueHD codec."
If that app didn't exist on the iPad, i'm not kidding when i say that i would never had bought one, as the Retina screen is obviously built to enjoy very high quality media; videos and photos of the highest resolutions. If i didn't find an efficient way of playing all video formats on the iPad, i would have definitely bought the best alternative by getting an Android-powered device, since Apple, by default, does not support many video formats. Especially with the overwhelming popularity of the MKV video format, which is still unsupported by all iPads. To overcome this problem, most sites that i've come across, just show a bunch of tutorials for converting your videos into iPad-compatible format, but this is so WRONG! I paid for an expensive piece of hardware and if it can't just play what i want, i might as well just go with an Android device, which plays most video formats using the default media player. I don't want to have to wait hours to convert movies. And what if i want to watch 3 or 4 movies in a day or everyday? I would have to convert videos on my computer 24/7. That's definitely not a practical or energy-efficient solution. The answer to this problem lies in third-party movie player apps which contain the required codecs and can play the videos directly without me being forced to do any conversion prior to copying the video files onto my iPad. That's the right way of doing it and the only way it should be (unless we start finding free iPads in our cereal boxes, in which case we couldn't complain about the lack of media support)!
2. GoodReader $7.98
This is the swiss pocket knife of file managers. It opens practically all file formats with ease and handles them superbly. A very wise choice if you don't want to have to look for an app every time you want to open a particular type of file.
3. Pages $9.99
The official word processor for iPad developed by Apple, so i guess that speaks for itself, in terms of quality and features. There are other more "complete" (and more expensive) premium office suites by other developers, but Pages is an excellent starting point, especially if you simply need a word processor with the best compatibility, fastest response, continued support via updates, bug fixes, etc.
4. Infinity Blade 2 $6.99
Finally, the best game (i know it's a vague term as some people prefer other types of gaming genres, etc) but it's an exclusive iOS third-person fighting game made by one of the world's best game studios (Epic Games) and it's the closest to ever be able to showcase (and impress yourself and your family/friends) with the CPU and GPU strength of the latest iPad (not applicable to iPad 1 and 2, as Infinity Blade 2 has been reported to not play as smoothly, compared to iPad 3 and 4). The visuals are simply amazing. It looks like a game running on the PS3 or Xbox360. The game itself is quite entertaining on top of having gorgeous graphics. On the iPad, you will not see better gaming graphics than with that exclusive game. There's a sequel coming up soon, so keep an eye out for Infinity Blade Dungeons.