One of the best freeware solutions I've found so far for downloading almost any type of media (audio or video) is Orbit Downloader. It "sniffs" your browser and watches for all requests for any type of media files (including flash of course), so you can easily download them. It supports rtsp streams and even supports rtmp streams (whereas VLC doesn't).
Some sites like imeem. com are using "anti-leech technology" which is just a stupid catch-phrase for a cheezy technique where the link they send you for the media file is a temporary alias to the real file on their servers, which they only allow you to access ONCE. That means a program like orbit downloader (or any of the other downloaders previously mentioned in this thread) won't be able to download it, because your browser has already started downloading the file, and you can't access the file a second time.
So for those special cases I've found that "Free Music Zilla" works great--it can get around the anti-leech technology by saving the file as your browser downloads it. And despite its name, you can easily configure it to work with all media files, including flv (flash files).
This is my first post so I can't give the websites, but you can google them and find them. And of course I'm not affiliated with them, I just think that so far I think they're great to use.
