My last phone (Samsung I760) would let me send calls to voicemail by pushing the end button. Is there any quick and dirty method of doing this with the Moto Droid?
I believe you are referring to an "incoming call," If so, push IGNORE and it should go directly to Voice Mail.
On a side note, you can send annoying contacts directly to VM by checking "Send calls directly to voicemail" when editing a contact.
Where is "IGNORE"? When the phone rings, it has a green icon on the left and a red icon on the right. To answer the call you slide the green icon to the right.