I was wondering this myself.  I signed up for an e-mail alert system that is supposed to let me know when an online retailer gets some in stock.  I guess I'll have to see how that goes.  I'm not sure if it would be considered spamming to name the site, but if you google "wii finder" or somthing like that, you will get a lot of results.

It will depend on your area. What stores you have near you, when they get shipments, if they are holding them for some future sale (as lots of retailers seem to be doing), etc...

For my area its Wal-Mart as we don't have a Target and EB Games/GameStop won't have Wii's to sell until February as they say they are filling pre-orders in my town until then. I got mine at launch, so I don't have to worry about it now.

A little suggestion; if while your looking for a Wii and you come across controllers, I would buy an extra set or two. It seems that the majority of the retailers have not been getting very many shipments in of controllers and most keep saying they don't know when they will get any... My local Wal-Mart has gotten 4 shipments of the Wii System in and 0 controllers since launch. I didn't buy any at launch cause I figured I would wait a few days and go get 2 extra sets, but that was a mistake. I have Excite Truck, SMB:BB, Madden 07, Wii Sports and can't play multiplayer yet.