If you're looking for grandiose and fun(ny) I saw a very successful one on the bridge in front of Splash Mountain that culminated with a minor soaking right after she said "yes".
If you're looking for quiet/romantic, there is a garden in France in the World Showcase where Sleeping Beauty does autographs occasionally, but for the most part it's extremely quiet and picturesque. My wife and I have used the space for a quiet 10 min lunch, and during that time only saw 2-3 other people which was nice. (Go into France towards the Eiffel Tower, turn right through the perfume store and go through it, and you'll be in the garden I'm describing.
Also, depending on time of year/day you could end up on certain rides alone. In October, it shouldn't be too hard to end up on a boat ride in The Land, or even in Mexico at Epcot just the two of you. They're relaxing, and interesting - something different.
Good luck to you! My wife and I will be there in mid-October too! Great time of year at the parks!