It has been stated to some extent, but the primary targets of Simple Beam are going to be pokemon with lackluster abilities, or abilities that only matter for the first turn. Examples.....
Slaking = demon bulk up beast, add slackoff and you have a pokemon with great bulk, a buff, and a heal to let him use it twice to rule the world. If you want to be mean add amnesia for a defensive monster
Archaeops (or however it's spelled) = DOES NOT HAVE DEFEATEST :D even if it doesnt get any/many boost moves, losing defeatest is worth it.
Any slow pokemon with sturdy. Opponent goes first, tries to take out both pokemon, aiming for your simple beam target with a super effective move, sturdy kicks in, it lives, gets simpled, takes its boost, chuckles at the end result next turn depending on what boost it used.
Any pokemon with switch in moves like Indimidate, Drizzle, Sand Storm, Drought and the like.
My final and favorite options are any pokemon using a multi booster, preferrably Dragon Dance, Quiver Dance, and Shell Smash.
I quite enjoy this combo with Crustle because of his move pool... double power shell smash with Rock Wrecker and x scissor stab with possible additions of night slash, earthquake or aerial ace for some decent coverage. Even Carracosta with 30 base speed could shoot up to as much as 537 speed, which is more than respectable.