While I agree that the Nikon D90 is a brilliant camera and probably takes the best quality still photographs in its class, it cannot compete with Canon cameras for truly professional grade film quality video.
If you can afford it, buy the Canon 5D Mk II which has a full frame sensor. The Canon 7D, the 60D and the 550D have equally good picture quality, but have a micro 4/3rds sensor and diminishing feature sets and capabilities.
The only feature differentiating these cameras than ones 20 times their size and cost is capturing shoots in RAW format... I guarantee that you will not be able to differentiate picture quality.
The Canon cameras mentioned above are, in fact, so good that they have been used by professionals in renowned TV serials such as HOUSE and 24, amongst many others!
Check out the DSLR Film-making course at FX School in Mumbai if you want to learn how to fully use such cameras and the full workflow associated with it... they are perhaps the only institute in India teaching film using this type of equipment... their students (many of whom are my friends) are now also working on live films with big name film-makers such as Ram Gopal Varma and others whom I cannot mention yet due to confidentiality reasons...
Hope this helps... Good Luck!