Liliputing checked Buy.com, Amazon, B&H, TigerDirect, Newegg, and Best Buy, as did we. All of those vendors have listings up for the Transformer, but none of them actually have the system in stock right now. Newegg doesn't even let you pre-order, while Best Buy says "sold out online," suggesting Asus didn't miss the launch and that the Transformer was in fact available for a short time earlier today.
If you're desperate for an Eee Pad Transformer right this instant, a few sellers on the Amazon Marketplace claim to have the device in stock... but they charge quite a bit more than Asus' $399 suggested retail price. The cheapest is $549.99 before shipping, while three other sellers charge $579. It doesn't look like those vendors are bundling the device with its optional keyboard dock, either. Faced with the choice between a $550 Eee Pad and a $500 iPad 2, I'd probably go for the latter.