Since it saved my Dad who was recently declared cancer free and no need for an oncologist - the colonoscopy. It is also diagnosed my husband before his Crohns needed surgery.

And for drugs, I love tPA for giving me back a 91 year old Mammaw and not a vegetable after her massive stroke. Chemistry can really rule!

More silly:
Air Conditioning
The wheel so I can get to work and ride my bike
Birth Control
Daily Contacts
DVR and the on screen tv guide
Hair Dye - I am totally not ready to embrace my white hair