Most effective and free weight savings is removing the foam, because it holds a LOT of water and takes weeks to fully dry. This has been discussed at length.
Cost per pound of weight savings skyrockets after the obvious $$$-level items like can, battery, and lightweight clutch mods mentioned above.
Don't forget track... run a 2.75" to save pounds over the 3".
Another thing that's not discussed much, but is significant when it comes down to riding, is what you carry on the sled and where. Tunnel bags, packs and bar bags can add up quickly. Carry what you need for emergencies and repairs, and leave home what you don't.