Here is a list of approved and declined mods. If you would like to use or suggest one you do not see please add it in the comments with a list of what the mod can do. Please include everything.
What the mod does:
All uses (inc extra features):
World Edit CUI (A handy tool for using World Edit, World Guard and claims)
Performance Mods like Optifine (Increases performance for some users)
BetterSprint (makes sprinting easier, it's allowed since vanilla sprinting is already very easy)
Mods that list all of the items (Makes it easier to look up recipe's)
5Zig PVP mod (Does not give an unfair advantage)
Any minimap that does not show players/entities/cavemode. (Does not give unfair advantage)
Shaders Mods (No effect on gameplay)
Capes Mods (No effect on gameplay)
Better Animations/Player Animations Mod (No effect on gameplay)
Blocks3D Mod (No effect on gameplay)
Gamma/Brightness mods (You can change the brightness to have no darkness in vanilla Minecraft anyway.
Info mod (Zombe's Info mod or similar)
Compass mod (Shows you your coordinates and heading in GUI)
Any Chat Mods (That have no effect on gameplay and do not spam the chat like Tab Chat or Chat boxes)
Any Protocol Mods (Lets you join outdated/updated servers)
Any Durability GUI Mods (Lets you see item and armor durability in GUI)
Any Custom Content Mods (Since the server does not have the mods installed they don't work)
Any Mods which have no effect to gameplay such as Pixelmon or Auto-Respawn.
Autoclicker (Lets you click much faster than normal also prevents you from being kicked for AFK)
Cheat Clients (Gives unfair advantage)
Fly (Lets you fly in areas you shouldn't)
Speed (Lets you speedhack)
Kill Aura (Lets you hit people outside of viewing angle)
Tracers (If they let you see sneaking or players outside of viewing angle)
Noclip/Wallhack (Lets you walk through walls)
No knockback (Unfair for PvP)
If a mod gives you an advantage over someone who doesn't use that mod, its most likely banned.
If a mod is not on this list it means it has not been evaluated, please ask below before using it to avoid confusion and possible penalties.