DVD Ripper

On Ubuntu, several tools are available. The following three can be installed right from the application menu.

dvd::rip

I recommend this tool, because it's fast and has a lot of options for tweaking the final output.
+ It lets you encode with several codecs
+ lets you specifying the final movie size
+ visual clipping and scaling
+ normalizing audio, multiple audio languages
+ subtitle handling
- Only supports 3 container formats (Avi, Ogg, Mpeg), not Matroska f.ex.
- Audio only in mp3 or AC3, not AAC f.ex.

Install note:

You should install additional software for being able to use all features:

sudo -i
apt-get install xvid4conf

AcidRip DVD Ripper

- Only Avi and Mpeg container
- Doesn't save your setup
- A bit confusing interface

Thoggen DVD Rip

+ Quick and easy setup of encoding
- Only supports Ogg for audio and Theora for video
- Slow encoding