Great Downloader easy to use can convert into multiple file formats. Fast and impressive
Downie - Video download for OS X. Downie supports at this moment over 1,000 different sites.
Video DownloadHelper - Browser extension to download videos from the Web
youtube-dl-gui - A cross platform front-end GUI of the popular youtube-dl written in wxPython.
JDownloader - JDownloader is a free downloading tool that enables you to download files from over a hundred hosting sites. The tool is compatible with Linux, Mac and Windows operating systems. Read more about JDownloader.
Youtube Video and Audio Downloader - Download YouTube videos in all available formats and extract the original audio files.
aTube Catcher - aTube Catcher also can burn in DVD/VCD your videos without use any other third party software.