I've been reading up on the differences between the Nikon D70s and Canon 30D and there is no real difference other than price and lens compatibility.
I read that with an converter you can use Nikon lens on a Canon camera, but you cannot do the reverse.
Given that you already have a feel for Canon cameras over Nikon ones, I'd go for the former. The built-in flash on any camera is near-useless anyway.
(I may be biased, because I've already decided to save up for a...