I got bored of Oblivion a while ago, but have started playing again. I really recommend getting the Imperial Thievery Mod, Midas Spells Mod, White Tower Mod, and Servant of the Dawn.

Imperial Thievery adds new quests where you steal stuff in the Imperial City (kinda obvious right?) Servant of the Dawn adds the Mythic Dawn as a new faction with a complete faction quest line that takes place after the main quests. These 2 alone add a ton of content.

Midas is awesome since you get tons of new spells and spell effects.

White Tower is great because you get a very awesome home for free (just need to kill a demon or two) and outclasses any of the vanilla homes and most of the player created ones.