They take a while to drop when you need them but when you don't need any you will pile up a collection.
http://us.battle.net/d3/en/item/ramaladnis-gift
I don't know what A.L. means here. If you are running with the Wizard weapon/source set you want to use this belt.
http://us.battle.net/d3/en/item/fazulas-improbable-chain
The 3 main jewelry sets are Legacy of Nightmares (2 rings), F&R (2 rings), and the Endless Walk (1 ring 1 amulet). Almost every damage build uses one of these.
Everything is a trade off. And dead characters do no damage. With that said, one chest/pants gem will not make that much of a difference. If you are talking about the helm gem it has different effects for Topaz anyway.
Also, if your recovery is low or does not scale with your max life (% boosts) you are probably better slotting diamonds instead of amethysts for survivability.