Don't forget too that you don't always want or need to capture the actual sun setting - there are some really neat shots opposite the sunset, capturing the warm glow on buildings, or to the sides of the sunset where the warm orange glow of the sky backlight buildings or subjects.
For pure setting sun shots, I like the Tomorrowland path to the castle for a castle shot in MK, and a Cosmic Ray's patio shot looking at Main Street. In Epcot, anything standing around Mexico to Norway will give great views across the lake to France, Morocco, Japan, and even US with sunset backgrounds. In AK, I like the sun setting over Flame Tree from Everest, and Everest sunset glows from Flame Tree.
For those other odd sunset-time shots that don't necessarily involve the sun itself, look for details to silhouette, or structures that tend to really capture the glow (Hollywood Tower Hotel, Everest, Thunder Mountain, Norway's Stave Church and Mexico's pyramid, etc) opposite the sunset.