First off, i would recommend using Nexus Mod manager and getting your mods from the Nexus mod site (not the steam workshop, that barely has any good mods).
For graphics, Skyrim HD - 2k textures (assuming your computer can handle the mods of course)
http://www.nexusmods.com/skyrim/mods/607/?
- Start with this one, if you like modding skyrim and want it to look amazing, look into ENB textures/ graphical enhancements. These are more difficult to install but look awesome.
Magic, Apocalypse - Magic of Skyrim, adds lots of new spells making playing a caster more fun
http://www.nexusmods.com/skyrim/mods/16225/?
SKSE and SkyUI for better menu navigation (SKSE is needed for a lot of good mods)
http://skse.silverlock.org/
http://www.nexusmods.com/skyrim/mods/3863/?
That is all i could think of off the top of my head while at work, will update with more when i get home.
Or look at this list and pick for yourself
http://www.reddit.com/r/skyrim/comments/1ttgm1/comprehensive_list_of_the_best_mods_for_skyrim/
I used a similar list when modding my game.