After watching the video features of the new Canon 5D mark II, I tought "Hmm, let me see if i can do that with my XSi", so this is a preliminar video test i did at night, soon i will do a more better test (something like Vincent Laforet did).

I notice, like the Canon 5Dmk2, with a canon F1.4 lens and ISO1600 i could capture very low light and even the city at night look impresive (you can even see the mountain at night, imposible to capture in a handycam), only that in HD you can see some chroma noise in the dark areas, at ISO800 look better but darker.

This is the cheapest way (with just the 600$ XSi body and a 90$ 50mm F1.8 lens) to have a nice "film-like" depth of field and also capture in an incredible low light conditions. Of course this is a APS-C camera, with the 5D mk2 full frame sensor and ISO up to 25600 will look a lot much better!