Hi,
You will have four options for playing Vvid/Divx/mkv files on ipad.
1. Use AVplayer HD (as the gentleman before me suggested). It is amazing especially with the recent upgrade, which is specifically for the faster ipad 2 A5 processor. So you can actually play 720p mkv files in it. I do not have much problems with it and I love it.
2. Cinexplayer - This is a great app as well. I got this when it was free. But this App only plays Divx and Xvid files but does not support AC3 audio format. If your movie/TV show is ripped with AC3 audio format. you'll just have a video with no voice. They do not support MKV files at present, but are expexted to update it soon.
3. VLC player - This also I got it when it was availble on the App store. (Now sadly it doesn't). If you manage to gain access to it then great. This has a wider playing format. But I have had trouble playing HD movie with this App. Not as smooth as AVplayer HD.
4. The last option is to convert all the files to a suitable format (A very tedious process). Use handbrake, which can easily convert your video files into iPad format. Using this you can just use itunes to upload the converted videos into video player easily.
One Last thing, Both AVplayer HD and CineXplayer have better UI for managing files, including deleting it directly from your ipad 2.
I know that most of this options have been mentioned in the above posts. I just thought of giving you a complete idea as what all option you have for playing a ripped video.
Note: there many other players available, but with mixed reviews. In my opinion AVplayer HD is the best availble to play many formats, including HD.
I hope this helped..