HandBrake

HandBrake is an open-source, GPL-licensed, multiplatform, multithreaded DVD to MPEG-4 converter, available for MacOS X, Linux and Windows.
Screenshots of 0.9.1: Click Here
Supported sources:

• Any DVD-like source: VIDEO_TS folder, DVD image or real DVD (encrypted or unencrypted, but protection methods other than CSS are not supported and must be handled externally with third-party software), and some .VOB and .TS files
• PAL or NTSC
• AC-3, DTS, LPCM or MPEG audio tracks

Outputs:

• File format: MP4, MKV, AVI or OGM
• Video: MPEG-4 or H.264 (1 or 2 passes or constant quantizer/rate encoding)
• Audio: AAC, MP3, Vorbis or AC-3 pass-through (supports encoding of several audio tracks)

Misc features:

• Chapter selection
• Basic subtitle support (burned into the picture)
• Integrated bitrate calculator
• Picture deinterlacing, cropping and scaling
• Grayscale encoding

Credits
HandBrake uses a lot of (L)GPL librairies from the Linux world:

• liba52 (AC3 decoding)
• libavcodec (picture cropping, scaling and deinterlacing, MPEG-4 encoding)
• libdvdcss (CSS decryption)
• libdvdread (DVD navigation)
• libfaac (AAC encoding)
• libmp3lame (MP3 encoding)
• libmp4v2 (MP4 muxing)
• libmpeg2 (MPEG-2 decoding)
• libogg (OGM muxing)
• libsamplerate (audio resampling)
• libvorbis (Vorbis encoding)
• libx264 (H264 encoding)
• libxvidcore (MPEG-4 encoding)

HandBrake