It's the little things that are great:
First off, you need a program to manage your mods. NMM is weak. If you have basic knowledge of computers use wrye smash. http://skyrim.nexusmods.com/mods/1840
Glowing ore veins....so you can actually see ore. http://skyrim.nexusmods.com/mods/193
An improved map, with roads. http://skyrim.nexusmods.com/mods/4929
Better sorting of items, more logical and intuitive. http://skyrim.nexusmods.com/mods/2730
Use the above sorting mod in conjunction with SkyUI for a MUCH better play experience. http://skyrim.nexusmods.com/mods/3863 <<---highly recommended improvement to the UI. Again, use with the above better sorting mod.
Simple and fun, adds more kill moves. http://skyrim.nexusmods.com/mods/10906
Bored with the same intro every time you make a new character? Alternate start, its great. http://skyrim.nexusmods.com/mods/9557
Like to role play? An AWESOME camping mod. http://skyrim.nexusmods.com/mods/10573
Want use for all the food and water in the game? Basic needs. This mod is light, simple, and not intrusive. http://skyrim.nexusmods.com/mods/10843 . Settings are configurable.
Followers are dumb. The fix? UFO. http://skyrim.nexusmods.com/mods/14037
You can't carry enough [censored]. This mod adds craft-able bag and pouches that appear on your character and look fantastic. http://skyrim.nexusmods.com/mods/16438
Combat is too easy. http://skyrim.nexusmods.com/mods/5485
Improved vampires. http://skyrim.nexusmods.com/mods/20370
And last but not least, if you're feeling ambitious and want a game where it is almost un exploitable and better designed skill trees. ACE. http://skyrim.nexusmods.com/mods/10037 This is a big change, but shouldn't effect your fps at all. I highly recommend it!
So many, I'm sure I'm forgetting some. Those are some of the "simple" mods that I use that I can't see having any effect on your fps. I use many others, but they are bigger and a bit more complex.