Hey
im a firemage raiding Black temple and Mount hyjal atm, and I was wondering what the best rotation is, now im just stacking scorches and using fireball untill the debuff is about to expire and i renew it, but it isn't working so good, i can only do about 1400 dps with 1187 firedmg buffed,91 haste,34.87% Critt and hitcapped ofc.
Any new ideas would be great :)

I'm not a high skilled Fire Mage, (Only visited a small part of SSC and TK.)

But In my opinion, find a Warlock and bribe him to use Curse of Elements.
Then threated the Raid Leader you'll constantly try to overaggro unless you have a Shadow Priest in your group.
And finally, make your fellow Fire Mages believe your going to help stack up Scorches, but just use Fireball whilst they're bothering about Scorches.

On a serious note, I've heard alot of rumours saying that going Arcane is an option for increased DPS if you get the 2 set of T5.

Unfortunately that's it my friend.. I was in a SWP guild until I quit the game a few weeks ago... Stack scorches, fireball spam until u need to renew, Hitcapped > Haste > Crit > Damage... *Note Diminishing returns applies to Spelldamage and not Crit* :) Hope this helped

Basically what you're doing is correct. Try to get a shadowpriest or at least a resto shaman.
And make sure you've got your coolodwn up for below 20%. Flamecaps and destropots also help a lot for dps.

You might want to try adding more haste to your gear if you can and start working around a 0/40/21 spec to obtain the touble Icy Veins to increase your dps a bit, most effectivly used together with a bloodlust as you'd have a full 40 second icy vein to go with the entire duration of the BL (pref, sub 20%). Im sure you'd do more than 1800dps on every boss out there approaching them with the right spec and group buffs used at the right time. The dps rotation depends on the fight, if you dont move, make sure the scorch is up and just hammer that fireball key, keep your ignite running (pray to the rng gods) and just have fun :)