Definitely spend lots of time at your resort's pool!
I also looove shopping at DTD! And at night there's usually excellent live entertainment! And for $18 for adults and $12 for kids, you can go up 300 feet in the Characters In Flight balloon and get some fantastic views of all of WDW!
Resort hopping is fun! I love checking out all the Disney resorts! You can hop a bus to any Disney resort from DTD. I usually bring a camera and walk around the resorts taking pictures. You can also eat (either QS or TS) at the different restaurants in the resorts. Some of the resorts even offer character dining... so you can see some characters without going to the parks! The adults in your party can go bar hopping at all the different resort bars! Also, I'm pretty sure all the resorts have those flat penny machines... so you can add to your existing collection, or start a collection! I don't know if you collect Vinylmations, but all the resorts offer Vinylmation trading...which is so much fun! While resort hopping, I like to ride the monorail around the resort loop! From DTD just hop a bus to either the Poly, Contemporary or GF. Do some shopping, go to the bar, grab a bite to eat, or just wander around the resort for a bit! Then hop on the monorail and ride over to the next resort on the loop and do the same! Then hop on the monorail again to visit the last resort on the loop. Then from there take a bus back to DTD!
Visit the Boardwalk! There's live entertainment (magicians, jugglers, musicians,etc.), shopping, carnival games, nightlife and dining. And you can see the IllumiNations fireworks at Epcot from the Boardwalk each night! You can also rent bikes to ride around the boardwalk area. It's definitely worth checking out!
On Wednesdays-Saturdays, hop the boat from DTD over to Port Orleans and catch a performance by Ye Haa Bob Jackson at the River Roost Lounge at Riverside and Elliot Dyson at Scat Cat's Club at French Quarter.
Play some mini-golf at one of the golf courses! Adults are $12.52 a round and children are $10.39 a round.
Visit the Polynesian beach one night and catch the Magic Kingdom fireworks from the beach! The view is gorgeous! And they play the music on the beach! Then stick around for the Electrical Water Pageant at 9pm!
You can also sign up for a DVC presentation. It's a sales-pitch, but you get a Disney gift card for going! And they provide transportation and child care.
Most of those suggestions are free or cheap (well... I guess that depends on how much you spend on shopping and dining!!!) But if you don't mind spending money, there's plenty of other things to do outside the parks like parasailing, waterparks, boat rentals, DisneyQuest, fishing, driving racecars at the Richard Petty Driving Experience, Cirque du Soleil shows, fireworks cruises, horse-drawn carriage rides, and even surfing lessons!