http://wiitracker.com is a great site to use, they list when any major online retailer gets them stock, plus the nice thing is that they list a history of when systems were available at different merchants, so you can get a patern, like Wal-Mart, they've been having their bundles in stock off and on today, it's $648, but it comes with 8 games that you can pick. The trick is though, to pick games that are already out, otherwise it won't like when you add it to your cart
They also have a PS3 finder linked on the page which is nice.
PLUS they offer RSS feeds, which is nice