As above.

Use iTunes

If they are not in an iTunes compatible format and you don't want to convert them, there are many media player apps that allow you to copy them to the iPad using iTunes I use CineXPlayer.

I use the AV Player HD app.

Same here.

Excellent app. Plays everything I throw at it.

Use drop box and can stream to IPAD without using storage space on the IPAD

You may need a lot of space on your Dropbox account for that, though, depending on how many videos and how big they are (& what else you store on Dropbox). I believe that that method also only supports iTunes-friendly videos (.mov, .mp4, .m4v), and not also .avi, .mkv etc.


For streaming videos, IMO better solutions are:

iTunes videos (.mov, .mp4, .m4v): Stream using iTunes Home Sharing, using iTunes on the PC/Mac, and the native Videos app on the iPad.

non-iTunes videos (avi etc.): Stream using a UPnP Media Server of some sort on the PC/Mac (e.g. PS3 Media Server or TVersity) and AirPlayer on the iPad.

just downloaded a free app called GPlayer.