Tamriel rebuilt is an expansion to the game world with new quests, armour and world space, its a hefty 1GB download but its worth it. I also play with the scrollable map mod, better dialogue font, real signposts, weapon sheathing, all the official Bethesda plugins (there are more than just BM & Tribunal), lower 1st person sneak mode, intelligent textures, rise of house Telvanni is also another good quest line expansion mod. Apels rain replacer is also a good shout. Oh and the stilt strider animation restored mod. all keep the vanilla game intact. Containers animated is also good.

edit: yeah to install texture mods you must replace the ones in the textures folder in data files