I just got my Visa to Germany.
You need:
1. AP or US visa to return
2. Invitation letter from the Germany company you will visit
3. Employment letter from your employer
4. Health insurance virification letter
5. Application form (go to German Consulate website)
6. Appointment(typically two weeks ahead)
7. Two passport photos
8. $92 USD fee
You can check other documents needed from German Consulate website.