My wife gets a lot of catalogs for things like bird food as a spin off from all the garden stuff she does. She got some "special" hummingbird food. The contents list had one item, sucrose. Yep, very expensive sugar.
On the seed front, I only know they have lots of blends tailored for various types of birds. I don't know much about it, but I would think scratch would be good for a lot of them.