4. Watch for system tracking sites
With the Xbox 360, tracking sites appeared that told you who had systems in your state. One site that will probably do this is www.ps3grabber.com, although the site has been down sporadically - and, right now, it's just tracking pre-orders. A few days before launch, do a Google search for "PS3 tracker" or "Wii tracker" and you'll probably find something that lists out which retailers have what.
One problem with these tracking sites, though, is that you never know if they are based on good information or not, so use them in addition to the other tips on this list - they most likely don't have access to actual Best Buy shipping manifests. Instead, most are just scouted by helpful (but error prone) volunteers.