What is the significance for eating Donuts on Chanukah Beyond the Oil connection?
Reb Shlom Zalman Auerbach in Halichos Shlomo Chelek Beis- Amud SHin Yud Tes: answers that we eat Donuts A mezonous food in order to Make an Al Hamichyah as in the AL Hamichyah we mention The Mizbach and we know that part of the Joy Of Chanukah is the Chanukas Hamizbach,The Gemara in Avodah Zara says that the stones the Mizbach the Chashmonim were unable to cleanse from its spiritual impurity so in a way its a memorial to the damage the Greeks caused.This also answers another question why we do not mention Chanukah Explicitly in Hamichya actually we do when we talk about the Mizbach. The Jellyhas a signifigance too, The gemara in Sotah says that since the Bais HaMikdash was destroyed the taste of fruits have never been the same. Fruit is associated with the Mizbei'ach as by bikkurim it says והנחתו לפני מזבח השם אלוקיך . Therefore we add fruit jelly to our donuts. (Shalmei Moed)
Sufganiyot are mentioned by Rav Maimon, father of the Rambam and he quotes the famous connection with cooking oil. A hint to their popularity in Israel can be found in an article in the Jerusalem Post which says that the Histadrut, worker's union, pushed sufganiyot instead of latkes because they're harder to make in your own home so it would force people to go out and buy them in local bakeries.
A nice article summarizing the arguments can be found here: