Some say dvd::rip is the most powerful application for ripping and encoding DVDs to save space.
I guess this depends on what you need from your ripping application. dvd::rip is a GTK-based application which offers a lot of features, supporting three containers (AVI, Ogg and MPEG) and several popular video codecs, like DivX or XviD; it can also extract DVD subtitles. dvd::rip allows you to select a target size and the number of files you want the video to be split, and it will also create an information file containing info like resolution, video bitrate, audio and video codecs etc. By default, dvd::rip saves created files under the ~/dvdrip-data directory.
K9Copy is the only KDE-based application which I could find (please share if you know some more), but it's good enough and a KDE4 port is also available. I liked that K9Copy handles subtitles, it allows you to select from a wide range of audio and video codecs, and it can create a custom number of files with a certain size (default is 700 MB x 1, but you can also create two or more files from a DVD, each one fitting on a CD). Overall, K9Copy is a powerful tool with pretty much everything you would ask from a DVD ripper and an easy to use, wizard-driven interface.
AcidRip is yet another GTK ripper and encoder, with support for subtitles and specific filesizes. AcidRip is an alternative for those who use GNOME and want to use something else than dvd::rip.
Thoggen is a simple application which encodes DVDs into Theora Video, the free video format from xiph.org. It has a basic and extremely easy to use interface, and it supports cropping, picture resizing, and selection of the desired size for the output Ogg file. The interface is so easy to use, all you need is to follow three steps: open the DVD location or DVD ISO image, select the desired chapters to rip and output file size, and then start the transcoding process. It has no support for subtitles. It is definitely worth a try, especially if you want your video files to be in a non-patented format.
Also built in GTK, HandBrake offers features similar with AcidRip, including x264 codec, subtitle support, AAC, MP3, Ogg Vorbis and AC3 audio codecs, and the possibility to select a custom file size for the output file. A guide for using HandBrake can be found on the official website, here.