Nintendo says Best Buy stores are already starting to get their first shipments in. But you still need to wait until Sunday to get one!
Nintendo issued a simple statement on their press site a few hours ago, proclaiming that yesterday (Wednesday) morning, UPS delivered the Wii consoles to Best Buy stores across the country. They included a photograph with this news, in case we needed proof of said event:

The early arrival of the systems doesn't mean you'll be able to pick one up any sooner than the November 19th launch date. However, you might want to consider slipping in to your local BB, breaking into the stock room and getting your Wii on a few days early thanks in part to the PlayStation 3 launch chaos.
Naturally, people are currently waiting in line right now for the PS3 launch, still about 30 hours away. Will people come out in similar numbers for Wii?