Walmart kicked just kicked off pre-orders via their web site.  They are currently showing as in stock, and will probably sell out within a matter of hours.  Keep checking via the direct link below: 

[edit - appear to be out of stock already!!!] 

Steps:

1)  Get clicking: Preorder Nintendo Wii at Walmart.com! 

2)  Select hardware on the left

Good luck, and let us know how you made out!