The recently released Canon 550D has a number of very important differences to the previous Canon 500D SLR for use for video work.
The main differences are the frame rates that it supports and that the Canon 550D now allows the use of an external microphone. The Canon 550D can shoot video at full HD 1080p at the same frame rates as the rest of the Canon lineup - whereas the Canon 500D could only shoot 1080p video at 20 frames per second. This was quite a limiting factor for the camera.
Overall despite the quite large price difference between the Canon 550D and 500D I would recommend the 550D as the preferred option for video work as it overcomes the crippled feature set of the Canon 500D.
