Great Downloader easy to use can convert into multiple file formats. Fast and impressive
Video DownloadHelper - Browser extension to download videos from the Web
CONV. - Convert YouTube video to MP3, GIF or MP4
youtube-dl-gui - A cross platform front-end GUI of the popular youtube-dl written in wxPython.
Downie - Video download for OS X. Downie supports at this moment over 1,000 different sites.
Youtube Video and Audio Downloader - Download YouTube videos in all available formats and extract the original audio files.
Yout - YouTube to Mp3 Converter