The normal contenders have put in-place a first-come first-served basis for sale of the Wii, including Play.com, Gameplay, and HMV. Interestingly, the website of the high-street based Game seem to force you to buy a bundle, and thus they won't be linked from here.
Most other sites are still taking 'register your interest here' submissions, including Amazon, and aren't allowing pre-orders like the stores above.
This Inq hack has already purchased his Wii and can't wait to get his hands dirty playing with it. µ
See also
Sony PS3 delayed in Europe
Wii splashes out at ¥25,000
First Wii CPus shipped