Aside from SI, KotN, and DLC expansions, I use a LOT of community-produced mods that it's taken me a long time to merge into a manageable number using TES4Gecko.
A fair number of Quest mods (IMHO, a quest mod is an addition to the storyline, offering a new or variant sequence of goals to advance something in the quest log), a great many additional item mods (increasing diversity in the number & type of items available), some mods that purely adjust the game mechanics (M.O.E., Intelligence Overhaul, some of Frans options), CM Partners (which falls somewhere between Quest and Mechanics, I'd say), texture and mesh replacers to both enhance appearance and increase framerate, and a number of cosmetic enhancements for actor and environment appearance.
My modded version of Oblivion bears
some resemblance to Vanilla, but it's a whole lot more than what Bethesda sold me for GOTY edition a year ago.