Besides for the Rambam (Maimonides), are there any other rabbis that are universally accepted and their sefarim are learned by all?

There is no difference between the Rambam, Rif, Rashi, Ramban, the ba'alei Tosofot, Ra'avad, Ritva, Ran, Rosh, and all the other classic rabbinical rishonim. All of their works are universally accepted, but in terms of practical halacha, since the acceptance of the Shulchan Aruch and Rama, on the issues which they wrote, they are from now on, the compositions upon which all others must relate (and even they, are sometimes subject of disagreement).