If you want your iPhone 4 to be black, you can now pre-order it from Apple's website for $199 (16 GB model) or $299 (32 GB model), together with the good old 8GB iPhone 3GS which is now $99 with a two-year contract with AT&T. Pre-orders are limited to two per customer.
Although Apple put the pre-order page up in the middle of the night (U.S. time), it still caused enough interest to suffocate Apple's servers, so you might experience slow loading times or complete unavailability.
Pre-orders are also available in the UK and France, but these stores are down at the time of this writing. Once they're back, customers will be able to buy an unlocked iPhone 4 which starts at £499 in the UK and €629 in France.