Feral Kitty DPS.
Affliction Warlock (I think?)

Other than that, as far as I know, every class is laughably easy to DPS as.

All classes are easy/accessible, and are supposed to be, but some definitely scale more with better play than others.

Shadow priests come to mind. The tighter you are with keeping your priority system and managing your DoTs, the better your DPS will be. Two shadow priests in similar gear can do significantly different DPS just based on who is the better player.

But hard? Nah. Wrong game for that.

As far as raiding,
Affliction Warlock (timing dots)
Mutilate Rogue (juggling multiple finishers)
Arms Warrior (priority based but with multiple procs to worry about)

Mages are pretty easy. Arcane being the hardest but it's still pretty much a regular rotation with one proc that changes one spell in the rotation.

All DPS classes are 'easy', but if you're the type who wants to squeeze every last once of DPS from your toon, then some classes are harder than others. I would count pre-3.1 affliction warlocks in that category.

I raid on my mutilate rogue, and I'll agree it was a little hard to get my dps going when I began playing, but pretty soon everything becomes routine. Nothing is too hard if it's part of your 'rotation' eventually is it? I can pretty much play with my eyes closed and fingers on WASD and my keybinds.

There are prerequisites (bleeds needed) for certain buffs (Hunger for Blood), but that's about the extent of it. I think the difficult bit while raiding with a melee class is actually movement, positioning (read not standing in green/blue/yellow/red crap) and sometimes judgement.

That being said, I'm not going to pretend I know (insert melee class here)'s rotation (But if it's a rotation, it's routine, and eventually, easy... right?)

Yeah, it's always the tanks and healers who do the hard jobs ;)

(Yes, I am biased)

And, just to clarify, yes dps are important, but really - tanking will always be the highest skill requirement, and healing generally requires the most effort.