Today, I have a game of 40K scheduled. I'm playing the studio Iyanden army against Ultramarines.
Reading up on the Eldar Rangers I found something really keen. They can be upgrade to Pathfinders (stay with me now). That give them, among other things, AP1 sniper shots if they roll 5-6 on the to-hit roll. It gets better. Sniper type weapons are now Rending, which has been moved to the to-wound roll (Sniper weapons always wound on a 4+ which is unbelievable against high Toughness targets). So, on a roll of 6 on the to-wound, they are also AP1.
This is a great weapon against Tyranid monstrosities.
I would definitely recommend a unit of five in any Eldar army. The models are great looking, for starters. In the game they are extremely flexible, durable, and deadly.