400d is an excellent choice, the new latest (500) has just been released, so the 450 and 400 will be coming down in price very soon, if not already
I would suggest going into a camera shop and physicaly holding the camera and the equivilent nikon etc, to make sure you get something that feels right to you
I've got a canon and know many people with them, but also know people with nikon's who rave about them, theres always some banter between canon and nikon owners, however whats important to you is what feels right in your hand, coz if it dont feel right, then that will effect how you take pictures
ps, its often cheaper online, but well worth a trip to a store to go play
also consider 2nd hand from places like london camera exchange (they have stores all over the country)