Hey Sarah,
Congratulations!! My graduation present was a trip to WDW. In fact we left a few hours after the ceremony. I had been talking about and planning the trip a year in advance.
We stayed at Pop Century and, when asked by the desk cast member at check-in if we needed anything else my dad replied "Do you do anything for those that have just graduated college?" He (the CM) then revealed that he had graduated the semester before.
A few nights later, after coming in from a day at the parks and Cirque du Soleil that night (another grad present), we returned to our room to find a card with the Pop Century logo on the front. It was lying open on our room table with balloons attached and a picture of the five main characters (Mickey, Minne, Donald, Pluto, and Goofy) in front of the castle with their autographs on the picture. The card also had their autographs on it, with "Congratulations, Kyle" at the top. I also made sure I bought the grad merchandise (the grad mickey that was mentioned before, a grad mickey antenna topper, and other stuff that I'm still paying for.)
But the card and ballons made my trip the more special, as it was personalized and signified a milestone.
You may also want to mention at any restaurant you eat or if you talk to any CM that you are celebrating your graduation. Of course, all of this is dependent upon the people you tell - they may end up not doing anything, but I'd be proud just to tell people about it.