if you're a canon fan and you can wait for about a month, the 450D is coming out. rumoured to have live view and all that, i think it's worth the wait.
the 400D is really old, however the newly released 450D will be expensive for a while, AKA the 400D will be REALLY cheap next month.
otherwise you should get the sony a100, I got it and I think it's a great camera, except the shutter sounds "wooden and noisy", and the flash doesnt pop-up automatically 😱😡😱😡
the price is comparable to the 400D/D40x. However sony is a real b**** when it comes to expansion. the shutter remote uses some random head, unlike the canon that has a headset jack which can be made from 5$ on instructables.com and you HAVE to buy sony's lenses (unlike others you can get sigma or other lenses however I dont recommend), while sony lenses may be a bit more expensive than the others, you know that you're getting quality stuff.
the a700 is also another option, but I'd wait for a newer model (probably will take another year or 2 to be released).