These Mods Can Help Whether You Are Experiencing Lag Or Low Quality Graphics

Optifine

Shaders

Minecraft Tweakers

These Mods Add A Lot To The Game

Tekkit

Minecraft Forge

Custom NPCs

SAO User Interface

Just Enough Items

Journey Map

Dynamic Lighting

You May Need

WinRAR

In Many Cases You Can Use 7Zip Which Is On All Windows Computers.