What's the most complete way to erase all the data from my phone so it cannot be recovered? I just got my replacement Droid and will be sending my current Droid back to Motorola.  I'm sure they are going to refurbish it and resell it.  I've backed up everything and I'm going to be keeping my microSD card, but how to ensure that all the data is completely wiped off the internal memory so there is no chance that it can be recovered by someone else?
Keeping the microSD is probably the main thing, so since that's the plan already it's just the phone to go. 

I couldn't swear to this, but I used it when selling my g1: 
uninstall everything - except astro file browser or similar
Use astro to wipe out any app related folders
remove astro
Use the "factory data reset" (on 2.2 its under Privacy)
Power up and check it's greeting you as a new user
Power off
Remove sim card
Power up and check it does even less
Power off &amp; send