So, you have a bunch of DPS. But what and who to take?
Clearly, as a guild leader or Person In Charge you cant know everything about everything. That is why you have officers however. But it is a good idea to have a few rules of thumb to run with if your Subject Matter Expert is unavailable and it falls to you to cover them for a night.
Hunters (max 4)
At the moment, Beast Master spec is the biggest hitter bar none. This will change very soon as they get liberally splattered with the nerf bat.
Mages (min 1)
Ensure you have your mages in the "right spec" for the fights you are picking that night. Having a frost mage if you plan on hitting bosses with frost resistance is probably not the wisest move. So plan ahead and ask your mages to respec if necessary.
Warlocks (min 1)
Locks can bring different things according to their spec. Demonology is a viable raiding spec again with felhunters having useful buffs. If you are taking more than one lock, try to ensure they have complimentary specs. The best option is to get them to sort it out amongst themselves.
Ele Shamans (max 1)
These guys are pretty gimped at the moment. Until they are fixed, I dont recommend taking one if you are struggling with your DPS output from the raid as a whole. I will update this with the patches and fixes later on.
Rogues (max 2)
Rogues do decent DPS and there are fights where their poisons are very useful.
Ret Pally (min 1)
Good DPS, solid buffs and good boss debuffs, make sure that the ret pally, prot pally and holy pally have complimentary specs and blessings.
DPS Warr (min 1)
In combo with the prot warrior this will take some pressure off the prot warrior to do utility raid shouts and debuffs and really focus on tanking. Get the DPS warr doing all that stuff. Respec if necessary.
DPS Death Knight (min 1)
These guys seem to be having some solid DPS and some REALLY great abilities (like deathgrip for malygos and blood aura in general) Try getting one of each main spec in there if you can.
But as you can see, its very generic and getting one of everything is a good idea for a raid. But again, we are now in the position that I would take a good PLAYER over a certain class as long as the 7-8 ranged and 6-7 melee is met. And even then, I have run very successfully with more melee than ranged and vice versa.