if you do a search on canon on here you'll find a thread on dslr's from a few weeks back.
in short, with any SLR, film or digital, you're really buying into a lens system, because the bodies will change every 18-24 montsh, but lens changes are far far less frequent.
IMHO, stick with canon, the lens choices are more broad, but like the old Mac. vs. PC debate, canon and nikon are both great, it's up to personal choice.
check out
www.dpreview.com, it's the digital photography equipment bible site.