1. Garchomp
A land shark... aka a nope. Garchomp is an awesome addition for a sweeper.
2. Flygon
Probably the most helpful one in my playthrough on Emerald.
3. Nidoking
With high base attack and easy to obtain, Nidoking is a great addition
4. Golurk
Golurk is an awesome addition to any team because he is a great wall.
5. Gliscor
Gliscor is great against grounds and lightning and is good for a lead pokemon.