Others may already know of this but I have just discovered the Blackberry Video Converter. I downloaded it from here and it has takedn a number of video .avi files and converted them into a format that works on my Curve.
I just started using Plato DVD Ripper. It is not free but it works great! I have a Storm and I have found it works with many different formats. I am currently using the setting:
iPod H.264 QVGA 320x240 768kbps Stereo
And the results are high quality. When I copy them to my media card I get a message that the "format is not supported and it is for transfer purpose only". But the Strom plays the files no problem. Using this format a 2 hour movie takes about 750MB of space.