A lot of the apartments in the area are (or have gone) Condo. There are only a handful left that are true apartment complexes. There really is nowhere that I can think of that will be as Grand as the Atlanta Developments that I have seen, but take a look at
Cagan Crossing. It is in Clermont (about 15 minutes from Disney on the backside of the property) off if Hwy 27 at US 192. The apartments are nice, we used to live there as do some of the other Diser's I know. They are in the process of building a Town Center which will have dining and shopping and the main entrance is right across the hwy from a Super Wal-Mart which is nice. The apartments are Nice, but not "luxury" persay.
These are not in a "development" as you are looking for, but Hunters Creek is a hot area. There is a lot right around there that you can get to fairly easily. The Parks at Hunter's Creek (we lived here too), Summit Hunters Creek, Colonial Grand at Hunter's Creek
These are right behind Disney, not really near anything without driving, but they are nice apartments and the area is in a stage of vast development: Alexandria / Parc Vue at Lake Buena Vista
Alexan at Legacy Dunes (we lived here too) are really nice, but I think they are going Condo, they also would require you to drive wherever you are going to.
Anyway, these are all right around Disney, I am not familiar with a whole lot of the Downtown area, I am sure that there are nice options out that way too. I think Hunters Creek would be a great area to start looking. It is a really nice area, not too far away from things and has lots of shopping and dining (you just can't walk to it). Anyway, I am sure others will have suggestions, but this is what I can offer right now. Also, some of these might be going Condo too, I am not sure!