Though the Android 2.0 'Eclair' SDK has been available for quite some time and the Motorola DROID runs Android 2.0 perfectly, the Android 2.0 source code has been kept under wraps for some particular reason (underhand deal with Motorola & Verizon?). This meant that all phone manufacturers outside of Motorola could only tinker with Android 1.6. Luckily, that has all changed.
Google has released the Android 2.0 source code to the Android Open Source Project and that's a great start for all Eclair hunters. Cyanogen has even got it fully running on his T-Mobile G1 and says everything is running "really well, fast and smooth". Eventually, we're sure that Android 2.0 will be available in relatively easy, how to instructions for rooted Android devices.