Handbrake (free; ) is great if you like lots of control (but that control can be overwhelming at times). RipIt ($20; ) is great if you like convenience and speed (depending on your requirements).
RipIt takes a much simpler approach than Handbrake. In RipIt's preferences, you choose the format you like your compressed movies to be in — either by device (iPhone / Touch, Xbox 360, PS3, iPad, Apple TV), or just the highest quality in a particular format (MP4 or M4V). This makes it really simple to choose the correct options since you know what device(s) you're going to be watching the movies on.
If you're just going to watch the movie on your Mac, you can just rip it, and the DVD will be stored as a .dvdmedia file, which is readable by Mac OS X's built-in DVD Player application. This file is much larger than the compressed movie would be, but it also contains the entire DVD: the movie, the menus, and the extras. If you're just going to watch the movie on your Mac, RipIt is fast. It usually takes around 20 minutes to rip a DVD to a .dvdmedia file. Compressing takes quite a bit longer (comparable to Handbrake's times, since it uses the Handbrake compression engine), and is required if you're planning on watching the movie on any device other than just your Mac. RipIt also simplifies the compression process by automatically selecting the proper DVD title to rip (unless you want to select a title manually), whereas with Handbrake you must choose the proper title on your own.