Supposedly dd_rescue is pretty reliable about ripping DVDs to .iso. There is also ddrescue which is a slightly different version of basically the same thing. I don't know much about them.
Personally I haven't found a single DVD that the current versions of VLC and/or HandBrake can't rip. However, these just rip the movie, not the full iso. Technically VLC doesn't rip it plays to a file, but when pulling a movie off a DVD the end result is the same.