I'll give you my top list:
1. Castillo de San Marcos. An old historic fort that you'll see on your way into town.
2. Cresent Beach/St. Augustine Beach. Relax on the sand. Tan. Enjoy yourself.
3. Shops on St. George Street. Yes, its very tourist-related, but fun. Lots of shops to wander around in.
4. Water cruises. Lots of these boats take tourist around the island for an hour. Beautiful.
5. Saltwater Cowboys. Good food.
6. Gypsy Cab Company. Awesome lunch place. Vote #1.
7. Fountain of Youth. A campy park based around Ponce De Leon's "discovery" of the fountain of youth and where they think the original landing spot was. Don't drink the water, but enjoy the scenery.
8. Bridge of the Lions. Its under construction right now, but look at some old photos of it before you go.
Things to SKIP:
- Ripley's Believe it or Not Museum. Very large, campy museum of oddities. Overpriced.
- Fort Mantanzas. If you've gone to the other fort, skip this.