One of the things that the Legend of Zelda video games have always done very well is create the illusion of the sandbox, while railroading the player along the prescribed storyline. It was the first video game that allowed for open-ended exploration (some twenty years before Grand Theft Auto, I might add) and had a save feature. Basically the idea is that the player has a big area to explore, but can't explore further until the dungeon is conquered and a MacGuffin is acquired, which in turn gives the player the ability to explore new areas and find the next dungeon.
I know I spent countless hours in every Zelda iteration just running around, trying to get a handle on the world that was available, and the resultant joy in having new areas to explore once I had the mechanical means to do so was always one of the best parts of the game. This is obviously a tradition I want to continue and draw upon for my Legend of Zelda 4e game with my kids, but I think the lessons learned here are applicable to any DM cooking up a homebrewed world.
Start with an area big enough to explore, and with some minor treasure to pick up, but make sure the players know there is a bigger world out there. Facilitate more exploration by giving them a mechanical means to do so. In LoZ, this meant acquiring bombs or the hookshot to get to new places. In more traditional D&D, this might mean clearing out the gnolls that control the pass through the mountains, or eliminating the necromancer in the old tower deep in the forest that keeps sending undead to kill the lumberjacks.
One thing that made the exploration so great was that persistence, curiousity, and cleverness was regularly rewarded with tangible benefits. Pieces of heart, bottles, bug-catching net, etc, that either granted additional prowess or opened up new options. This is definitely something that DMs should include in their games, especially as it rewards exploration and role-playing!
What do you think? Are there any video game tropes you've used to good effect in D&D?