Before (if) you ask, Oblivion is another Bethesda softworks game, which works in a very similar way. I don't know your tastes, but I'd recommend Cube and Mantis Imperative, two very good "dungeons", detailed, complex and subtle. Very professional. I'd also recommend xCalibr (weapons mod I didn't try it yet but it seems good) and ceasarrulez excessive interiors. (Always look at the requirements tho) Have fun ;-)