The Android Dev Phone 1, a totally unlocked G1, is available to "developers" for only $399 after paying a small setup fee. Just register as a developer over at the Android Market and the phone is yours.
Registration as a developer at the Market costs $25, but after that, you're eligible for the cheap, unlocked goodness. The Android Dev Phone 1 is fully compatible with Android 1.0, and being able to swap out the SIM card effectively breaks the yoke of T-Mobile's not-so-widespread service. It'll also let you flash custom Android builds that work with the newly unlocked bootloader. The phone even ships for free with fancy detailing on the back. Google warns that it's not really meant for non-developers, but we're sure that won't stop even the least adventurous Googler. [Google and Engadget]