OP: I would pick up Flamebringer's Crown from a quest (google it) till you can get the 40 Wintergrasp mark Titan-Forged Hood of Dominance, Hat of Wintry Doom is from tailors or AH and is also great with a Chaotic Skyflare Diamond in the meta slot. The belt is iffy and the Wyrmrest rep belt with 60 spellpower and 40hit would probably serve you better than the one you have. Frostsavage pants and bracers are also better options, again, look on AH or ask a tailor. Cleric's Linen Shoes from Nexus heroic will do you ok till you can get exalted Wyrmrest boots.
Valonforth's Remembrance is a pretty horrible mage trinket, it's more for healers. Cannoneer's Fuselighter comes from one of the quests at Argent Stand in Icecrown and will do you nicely. There's also a decent one from a Wyrmrest quest in Dragonblight, which also provides useful Wyrmrest rep. Another good one is Mark of the War Prisoner from Cyanigosa in Violet Hold heroic, and the one you can buy with heroic emblems, Sundial of the Exiled.
Get your Kirin Tor rep up first, wear the tabard in heroics until revered, that will give you access to a slightly better sword (Flameheart Spell Scalpel) and the +spellpower head enchant. (Arcanum of Burning Mysteries). After that, work on Wyrmrest rep. As an alternative to the Kirin Tor sword, work on Argent Tournament quests and get the +408 spellpower sword there. You'll want Kirin Tor revered for the head enchant anyway, though.
Your shoulder piece is fine for now, but I notice you have a +16int gem in there. Don't gem int, especially when your spellpower is so low. Unless you need a specific colour gem to activate a useful socket or meta gem requirement, gem spellpower or hit. It generally goes- Red spellpower gem for red sockets, (runed scarlet ruby), Purple spellpower/stamina gem for blue sockets, Orange spellpower/crit gem for yellow sockets, IF the socket bonus is useful. If the socket bonus is something useless like 2 spirit, just throw a runed scarlet ruby or runed bloodstone in there. You should also start questing in Storm Peaks and get your Sons of Hodir rep up for access to shoulder enchants.
Easy heroics to spam are Nexus, Utgarde Keep and Violet Hold. Those should get you started on badge gear and reputation. Also some nice drops for mages. Heroic Azjol-Nerub also drops a good belt, ring and wand, this instance really isn't too hard either as long as you read up on tactics.
http://www.wowwiki.com/Anub%27arak_(tactics)
I just did it for the first time yesterday, I had no idea what I was doing here but basically you just AoE adds when he burrows under the ground and run AWAY from the spikes coming up under the ground. Gotta love Blink and emergency Ice Block. Not as hard as everyone makes out, with a good group.
If you want to raid and not just do heroics, I would suggest respeccing to arcane as a starter spec. The best damage right now is fire supposedly with top end gear, but you are not there yet. The premise is to take 11 points in frost for Precision and Icy Veins, and the remainder in Arcane. During dungeons you'll either Blizzard packs of trash, or on bosses go Arcane Blast x2-3, then Missile Barrage if it's up or Arcane Barrage. Arcane/Frost works well for starting out raiding as you get +6% hit from your talents leaving you with less to work on in gear. You need 17% hit to be capped for raid bosses (look up hit rating on WoWWiki), which is probably why that group kicked you. You have 5% hit from talents and gear atm, which is pretty poor even for a pickup Naxx10. Think of it like ACC in FFXI- it's more important to be able to hit mobs before anything else. Your general priority should be hit until cap-> spellpower ->crit/haste->anything else. Adjust as necessary depending on spec, amounts available, and what you're lacking.
Look up arcane mage specs on the net. You are specced for frostfire bolt I guess? Arcane would be a pretty significant hit and spellpower boost. My spellpower goes up by about 100 just changing to arcane spec. Ebonweave robe and gloves would bring you up hitwise by a fair ways, as would The Argent Skullcap from a quest in Crusader's Pinnacle in Icecrown.
You should have np making money for all this with quest catchups, and herbalism and alchemy- Sholazar and Storm Peaks are mad cash, sell tiger lily and deadnettle on AH and spam Flask of the Frost Wyrm to sell when you can- but keep a few for your own use. You should also make your Mercurial Alchemist's Stone for a nice chunk of spellpower and haste, as well as a bonus to potions.
HIJACK TIME!
armory.wow-europe.com/character-sheet.xml?r=Shattered+Halls&n=Discordia -is how I am so far- horrible hat and iffy gear elsewhere, so I'm working on the Wintergrasp helm, trinket/belt/offhand from emblems, and Wyrmrest Accord exalted boots most of all. I'd like to know which is better between the alchemy trinket and Cannoneer's Fuselighter, and where I can get a better wand aside from heroic AN (very unpopular and hard to get a group for). I know I'm over hit cap buttttt I can't really swap anything out without being under cap again. Trying to get a couple more upgrades before I start any raids, any you can tell me?