I keep my movie collection on my home computer. It's way more convenient than loading a Bluray disc each time I wanna watch a movie. If you have an iPad, you can also watch your movie collection. Having VLC (Which I heard was recently removed by Apple...BOO!!!!) allows you to download an watch your movies on the go... but even the 64GB iPad can't hold all the HD movies you want.
This is where Air Video comes in. Install the app on your iPad (or iPhone/iPod Touch), then a small server program on your home computer. You have to keep your home computer on for the app to work since it allows you to watch the videos on your home computer. It streams the video to your iPad over your WiFi network.
It can handle HD (mkv), avi, mpg, and almost any video that can be played on your home computer.
Download Air Video from the iTunes App Store, then go to their website to download the server app (works on Windows and OSX)
*There's also a free version, the limitation is that it only displays 3-4 random files in your video directory. If you can live with that, then it works just fine as well.