I have two:
A few years ago I walked from my office to the shopping center next door for lunch. It was a massively hot and humid day, the parking lot had just been paved, and there was an armored car sitting outside the store to make a pickup. The combination of ozone and deisel exhaust hit me and suddenly I was at the bus stop at Downtown Disney. I stopped right there in the parking lot for a moment and closed my eyes just to savor the memory.
Some years ago I was chatting online with someone and pulled out a recent set of WDW park maps to check something. When I pulled them out of the cabinet, the smell of the printers ink was so fresh and strong that I was suddenly standing in front of the big park map rack at the Epcot turnstiles. Again, I sat still and closed my eyes for a moment to enjoy the memory.
Scent is one of the most powerful memory triggers, as is sound. I get these feelings from listening to some park music or watching my old vacation videos, too.