I'm guessing all your accessories are receiving power?
Turn the key on and jump the leads on the solenoid with either a heavy gauge screwdriver or wrench. If the starter engages, it's the solenoid. The solenoid is what clicks when you have a discharged battery. If the starter doesn't bump, I would look into the relay; if you have a multimeter, you can test these, but you'll need to find instructions on how to do it for your specific relay...Or you can just replace it since they're fairly cheap. I would say it's one or the other.
I believe that the solenoid is attached to the starter. I believe that the relay is mounted on the quarter panel with other relays. I suggest thick gloves when testing the solenoid. It doesn't happen often, but there have been a few instances where people have gotten an unwelcome shock by touching another piece of metal with the screwdriver/wrench while jumping those leads.