Addon Control Mods

!AWP ape47

In Game AddOn Manager, User friendly layout,
Profiles Save/Load (Account), RightButton click the checkbox of the addon to lockdown, Extremely lightweight.
WoWInterface

ACP sylvanaar

Allows players to turn on/off mods and reload their ui in game instead of needing to log out. Also lets players make sets of mods.
Curse, WoWInterface
Review: WoW Insider

Addon Loader Ammo, Cladhaire, mikk

AddonLoader is an addon that loads other addons automatically, as and when they are needed, which speeds up the logon process. Note that addons need to be aware of AddonLoader for this to work; if you see "X-LoadOn-..." tags in their .toc files, they are!
Curse

Ampere Tekkub

A small addon designed to mirror the functionality of the login screen "Addons" button in-game. It's designed to fit inside the config GUI introduced in patch 2.4. Amp lets you quickly enable and disable addons, reload the UI, and load LoadOnDemand addons.
WoWInterface, Curse, github

LoadIT Saur

LoadIT was designed to allow in-game management of your addons. Using LoadIT, you can enable, disable, and load addons during gameplay. You can create profiles of addons, and switch between these profiles on-the-fly. I designed LoadIT, because I have sets of addons that I use for instances like Molten Core, Blackwing Lair, and Onyxia's Lair, but I don't care to have many of them loaded while I'm in battlegrounds, due to the amount of lag some addons create during PVP.
Curse

stAddonManager Safturento

stAddonManager is a very simplistic addon that allows you to enable and disable addons without having
to log out. It has a search function for added convenience in finding a specific addon. To toggle the window, use any of the three slash commands (/stam, /staddonmanager, /staddon) or press escape and press the stAddonManager button in the Game Menu..
Curse, WoWInterface

TooManyAddons daxdax, messing

This mod is like an 'outfitter' of mods. Type a title and click new profile, select what addons you want to load with this profile, and whenever you click load profile the checked profile will load those, and only those, addons.
Curse