For spells: I have one key bound to twincast, force of elements, spear, spear, spear (3 latest ones), and storm of many. Other key is bound to remorseless servant, force of elements, spear, spear, spear....for when not using twincast. Burn key is AA's : Focus, First Spire, Fire Core, Elemental Union AA Twincast in there also.
To get a specific answer, the question needs to be more specific. The spell lineups I use for burns in various raid and group situations can vary pretty significantly.
My mage is only 100 but I use Relentless Servant, Rain of Blistersteel, Rain of Scythes, Spear of Blistersteel, and Spear of Molten Steel (Singles of course). If there is more than one I just pound out the Servant + the three spears I have access to.
If you're going for sustained (rains), you may look at Shock of Darksteel in place of lower Spears to follow them up. Its innate 25% to basically twincast via the Steel Vengeance AA gets its damage above Fickle or Bolt, for 1/4th the cost of 100 Spear.