Hmm... well, besides the Rending Rippers thing, the only biomorph I've seen used a lot is Hive Node. As for the Rippers, the Eldar are gonna have to bring Scatter Lasers, Starcannon, or triple batteries of Vibro-Cannons!
Exceptional Size is too expensive.
Weapons-Beast... well, once upon a time I thought Rippers could be mutated with Spore Mine Launchers (it *is* a bio-weapon, technically...). If your fleet is real short on variety, you can shave a point or two off you 'fex or Tyrant if you gave it a big gun...
Hive Node: Good if you want your Gaunts to roam, but it's not perfect... plus they make tempting targets for Swooping Hawk grenade packs! Which I have done... I've killed 4 Hive Nodes and about 10 other Gaunts with them alone in one game.
Acid Blood: I've never used it, but I've heard about people who have... personally, I don't like it.