There are some retextures ("Dark UI", "Oblivion Style UI", and more than a dozen of mods that tint the original UI in a different color. There are also retextures of inventory icons, the crosshair, and the compass marker. There are also a few mods that add new functionality to the interface, like zooming, or health bars for companions - these mostly require MWSE, MGE, or both. What specifically are you looking for?
Personally, while I tend to try one of the retextures every now and then, I always return to the original UI. I think it's one of the best UIs I ever saw in an RPG - nice, unobtrusive, easily adjustable, and quite efficient. The only thing I miss are filters/sorters for huge inventories, but that'd be very difficult to achieve.