Rooting your Motorola DROID
For 2.0 and 2.0.1
There is a great illustrated guide available at rootyourdroid.info.
This works on 2.0 and 2.0.1 only. Once you update to official 2.1, you won't be able to use this method.
Verizon is rolling out the 2.1 OTA update. It installs a new recovery image which disables the known method of rooting your phone. If you want to update to 2.1, do not wait for the OTA. Instead, use the method from AllDroid To obtain rooted 2.1.
For 2.1
This applies both if your phone updated to 2.1 with the OTA, or you got the phone with 2.1 from the store.
You'll probably need to go back to 2.0.1 and then apply the rooted 2.1. Instructions from Blogsdna have been reported to be reliable.
More detailed instructions from droidmod.