Good news for Nexus One fans in the UK, Singapore and Hong Kong, you can have the unlocked version of the Nexus One shipped to your country.
See below text that showed up when I wanted to order mine:
Please note that we do not ship US T-Mobile service plans outside the United States. Also we can ship the unlocked phone to the United Kingdom, Singapore, and Hong Kong. If you wish to continue with your service plan purchase, specify a US shipping address. If you wish to purchase a Nexus One phone without a service plan, you may specify a shipping address in the US, United Kingdom, Singapore, and Hong Kong.