Join Multiple Video Files of Various Formats Into One Movie

Say you have several short video clips that you want to merge into a single movie. The videos may be on the desktop or on sites like YouTube & MySpace.
If these offline videos are in standard Windows Media  or AVI formats, you can easily use Windows Movie Maker or Video Spin to join the clips. Just drag the clips onto the timeline and publish a new movie.

Now consider a more complicated scenario - you have downloaded a Flash video from YouTube, a 3gp clip from your mobile phone, an MPEG video from your digital camera and an MP4 podcast from your iPod.
How to you join these files of various formats into one video ?
One option is to convert all the videos into WMV format using a free encoder like SUPER - now join the converted clips using Windows Movie Maker, Virtual Dub .
The second option is that you join videos online using a service called movavi  - upload the files, select an output format and it will join the videos for you.
Movavi is especially useful if you want join several web videos from sites like YouTube, MySpace or Google Videos - you just supply the video URLs, movieavi will fetch the clips from YouTube onto their servers, join the clips and send you link once the merged movie is ready to download.