In anticipation of the eventual release of the PlayStation 3 in UK, I've made a PS3 stock checker. Sign up to be notified by email when new stock arrives. There's also a Nintendo Wii stock check page. Amazon.co.uk had it just this morning!
The Wii comes out tomorrow and unless you're willing to queue out in the rain overnight, or have a pre-order for tomorrow, getting one will have to wait. Luckily, there is an excellent site that will track inventories across the UK for new stock and alert you if you so wish - Nowinstock.net.