Life orb increases damage your pokemon does by 30%. But your pokemon will lose 10% of its max HP with each successful attack.
Choice band increases your pokemon's attack by 50%, but it may not change moves until it switches out.
Choice scarf increases your pokemon's speed by 50%, but it may not change moves until it switches out.
There are also the choice Specs, which do the same thing as the choice band and scarf, only it increases your special attack instead.