Blocks of Folsom St. and So. Van Ness have some beautiful Victorians. The small streets are really fun to investigate.
As Mario says everybody is different in what makes for appeal. Some of the best features are in the backyards too. I've seen some fantastic fruit trees and other wonderful gardens in the yards. Speaking of that, I'd put the well kept yard right up there with curb appeal for attractiveness. Looking out at nice greenspace is very appealing.