I have been pretty happy with the one from CUCUSOFT.COM, its a commercial program, but it seems to work pretty well. I tried a few before I found one that converted widescreen DVD's properly by not leaving the letterbox bars at the top and bottom of the video. Most programs left me with a 4:3 video file which couldn;t be zoomed in on properly, cucusoft actually produced a video of the proper acpect ratio which worked well on the iPhone. plus free upgrades for registered users as the add more features.
there is a version of handbreak for windows I believe if you want to go that route.
Download HandBrake 0.8.5b1
• For Mac OS X (Graphical, 10.4 or newer)
• For Linux (Command-line)
• For Windows (Command-line)
• For Windows (Graphical)
• For Mac OS X (Command-line, 10.3.9 or newer)
• Source code
I've also been using DVD Decryptor and Videora iPhone Converter and its been working great. Videora takes a bit to convert it and just a heads up, it will say 100% complete very quickly, but its not even close to done, just let it sit for a couple hours and it will notify you when done.
I use Clone DVD Mobile and AnyDVD, both from slysoft.com think you can buy the keys for both for something like 30 dollars as a package. I originally bought it for my ipod, but foundd it works for the iPhone as well (just drop the movie into iTunes to send it to your phone).
Thing I like most about slysoft is that the keys are good forever (well unless the company goes under), you can use it as many times as you want, and lifetime free updates on all their software. Might want to check it out. Just make sure not to by CloneDVD Mobile alone! you WILL need some sort of DVD decryption removal to use it (AnyDVD runs in the background and does this automaticly as soon as you put a DVD into your drive).
Ive been using their software for a few years now, and have to say they've done a outstanding job on supporting their software, unlike others I've tried. I don't mean to advertise for them, but been really happy with them.
I would also go with http://www.slysoft.com/en/. You can try them out for 21 days before you buy. Working version and all. There are updates all the time. Very good products. I have used them for the last 2 yrs.