From NPR, a searchable sortable archive of the best commencement speeches, from 1774 to the present. What a resource. Two of my favorites, by David Foster Wallace and Steve Jobs, are represented.
Each speech is tagged by "theme or take-home message", basically a taxonomy of commencement speech messaging. The most popular themes are:
12. Be kind
11. Yolo
10. Make art
9. Balance
8. Dream
7. Remember history
6. Embrace failure
5. Work hard
4. Don't give up
3. Inner voice
2. Tips
1. Change the world
Trite stuff perhaps, but delivered in the right way and by the right person, it makes people wanna run through walls. Let's go! (via @tcarmody)