Like you already said the Lati twins is a good one. Seen on 8/10 Doubles teams. Also something that resist a BoltBeam combo is kinda hard :P.
Lati@s only has problems with Ice.
Also Volcarona pops up in my mind, but she has a 4x Weakness against Rock but with the right support she can't be tamed. Water is easily covered by Giga Drain or any other Grass attack.