Andy Ihnatko's pick of the week on MacBreak Weekly 389 is MacTubes; a YouTube player and downloader for Mac. Simply copy the URL of the video from your browser's address bar, and paste it into MacTubes. Then it will give you a choice of what quality video you'd like to download or watch.
MacTubes can search YouTube as well: by keyword, author, or related videos. It can also create video playlists and show your play history. Playlists can be sorted by category, keyword, or author.
Since videos are taken down from YouTube because of copyright claims all the time, this is a great tool for preserving them locally on your computer. Andy points out that there are a lot of older TV shows on YouTube that technically aren't out of copyright yet, and could be taken down at any time.
To hear Andy Ihnatko give his recommendation of MacTubes, check out MacBreak Weekly episode 389.