The Lost Spires is a definite must, also
The Ruins of Tarnesia is a great dungeon mod, IMO it is THE king of ALL dungeon mods so far, the author did better job with the dungeon than Bethesda did with any of the vanilla ones. Kvatch Rebuilt,
Midas Magic Spells of Aurum,
High Rez Skin Textures for HGEC(Just a personal preference, there are several other body replacers also.),
Corean race mod, this way your characters won't necessarily look like old mummies no matter what their age is and simply the best looking 'human' race,
Ren's Beauty Pack includes 4 Mystic elf races; normal & tattooed, male & female, also there is a separate voice set for this made by bunsaki(?*) that can be found-->
here<--. The voice set only affects the player attack/being struck/fall down screams, if wanted, it can be used with other races aswell.(Using it myself.) Also there is a mod/are mods with complete voice sets and idle speech/power attack speech etc. it/they can be found--->
here.
OOO, UOP, deadly reflexes + sca combat mods conclude the rest of the essentials. Do mention if I've forgotten anything.