If you want to download YouTube videos on Mac or visit several video websites and want to download videos from each one, then iTubeX can help you both download and convert them.
iTubeX downloads videos from YouTube to your Mac and features it's own web browser meaning you don't need to open your default browser to view or download videos. You can browse any site such as YouTube, Metacafe or DailyMotion and download videos in a click. Just enter the URL of the page with the video you want to download and the select whether you want to download to MP4, FLV or convert. Conversions are limited to MOV, AVI and DivX and you can adjust the encoding quality.
It can be a bit tricky to work out how you actually download videos with iTubeX although all you need to do is use the download button in the top right corner. By default, it downloads in FLV but you can make it download in MP4 by (in YouTube at least) going to "View" in the menubar and then click '"Watch current YouTube video at highest quality" Then simply click the download button in the top-right hand corner.
On the downside of iTubeX, downloading is a bit slow although not much slower than most similar apps and you can't perform batch downloading.
Overall, iTubeX is ideal for downloading YouTube videos and others for Mac.