Hi Matt,
I would highly recommend the Canon 450D for DSO work as I've been using one for a couple of months. It is a great performer and works extremely well for an unmodded camera. The one real advantage it has over the previous DSLR's is the Live View function. I honestly don't know what I would do without it. It takes all the hassle out of focusing so that is a really big plus for when considering a new camera.
Another option is the Canon 40D or maybe even the new 50D that will be arriving very soon. These will be a step up from the 450D but also a step up in price as well.
If you are interested have a look at my website for some images I have taken with a Canon 450D and a similar setup to yours (C8 on EQ6 Pro).
http://AstroMatt7.googlepages.com/
Hope this helps and welcome to the dark side.
