Oh my gosh, there are so many things to do, I don't even know where to start.
You can get a cake or other sweet treat delivered to your room by calling Private Dining at your resort. To have a cake at a meal, call the Cake Hotline: 407-827-2253.
You could get flowers or a gift basket delivered by the WDW Florist:
http://www.disneyflorist.com/ They also do room decoration.
You could arrange a special treasure hunt or room decoration through Gifts of a Lifetime:
http://www.giftsofalifetime.com/
You could go on a carriage ride at Ft. Wilderness or Port Olreans, or a wagon ride at Ft. Wilderness. I think they have a haunted Hayride right now too.
You could rent Sea Raycers or go parasailing or just ride around on the boats that transport you to MK and the MK-area hotels.
Call 407-WDW-PLAY for either of those activities
You could watch fireworks from the Polynesian beach or re-propose at one of the wedding locations, like Sunset Pointe or the Yacht Club Gazebo.
You could go on a backstage tour (OK, I know that doesn't sound very romantic, but for nerds like us it was!). 407-WDW-TOUR
You could have Private Dining at your resort set up your meal on your balcony, or you could buy a picnic lunch from a food court and eat it on the grounds of one of the more picturesque resorts.
You could go horseback riding or fishing or just take a walk at Ft. Wilderness.
... how's that for a start?