I propose Walrein. It's bulky, has a good typing, and can use Surf well.
Walrein can be found as a Spheal in Shoal Cave, outside of Mossdeep city. It evolves into Sealeo at level 32, and into Walrein at level 44.
Walrein can learn Surf and make good use of it as a STAB move. It can also learn Waterfall and Dive. Walrein learns Aurora Beam by level up for those pesky Dragons, but I recommend using the Ice Beam TM.
It has great HP and Defenses, at 110/90/90 respectively. Unfortunately, it's pretty slow. It's ability in Emerald, Thick Fat, halves damage from Fire and Ice type moves, which is helpful for switch-ins.
Walrein (I recommend a held item like Mystic Water or Leftovers)
Nature and EVs don't really matter
Ability: Thick Fat
With these moves, Walrein can do well against:
-Tate and Liza's entire team
-Maxie's Crobat and Camerupt
-Sidney's Shiftry and Cacturne but be careful
-Drake's entire team
Walrein can also tank many hits and do powerful neutral damage to a lot.