Canon 450 or 30d?
I chose the 450D over the 40D, so would easily choose it over the 30D. But it depends what's important to you, whether this is your first DSLR, if not, what you're upgrading from, and so on and on. The 30D still will be better in terms of AF, controllability, and speed. The rear LCD on the 450D is noticeably better and I think the IQ will be at least as good. The viewfinder is slightly better on the 30D but the 450D's is just fine for all uses.
Why don't you consider a newer camera, such as the 550D or the 40D, 50D, or 60D?