There are actually several different flasks raiding mages can use, it will be up to you to determine which is best for your spec and needs.
Flask of Pure Death - By far the best increase to dps for Fire and Frost mages. +80 Fire/Frost/Shadow Dmg 43 dps increase.
Flask of Blinding Light - The Arcane version of Pure Death, much like that great Greek hero, you will be able to easily blind your enemies and take their lewtz. +80 Arcane/Nature/Holy Dmg.
Flask of Supreme Power - Sometimes you're a bit broke for the better flasks, sometimes you're so leet you only need +70. We won't judge you. +70 Spell Dmg 38 dps increase.
Flask of Distilled Wisdom - Not a very offense based flask, but does provide a nice increase to one's mana pool. Also for deep Arcane spec'd mages, this flask give ~75 int, ~18 spell damage, 1125 mana, and ~1% crit. +65 Intellect.
Shattrath Flask of Supreme Power - Obtained from either the Scryer or Aldor bank via Mark of the Illidari once you are Exalted with Cenarion Expedition, the Sha'tar and Scryers/Aldor. +70 Spell Dmg.
Flask of Mighty Restoration - If you have to wand for the last 80% of a boss fight, this may be the flask for you. +25 mp5.
Shattrath Flask of Mighty Restoration - Obtained from either the Scryer or Aldor bank via Mark of the Illidari once you are Exalted with Cenarion Expedition, the Sha'tar and Scryers/Aldor. +25 mp5.
Unstable Flask of the Sorcerer - Very good, cheap way to not only boost damage but also your other stats! Only usable in Gruul's Lair. +20int/+30stam/+23 Spell Dmg. 14 dps increase.
If you so choose to do so, you may dual elixir during raids instead of flasking, but it's best to have both a battle elixir and a guardian elixir up for every pull.
Adept's Elixir (Battle) - The added crit can be helpful, and is quite tempting considering none of the above flasks feature crit. A solid and cheap elixir choice. +24 Spell Dmg+/24 Spell Crit 20 dps increase.
Elixir of Major Firepower (Battle) - +55 Fire Damage, the elixir that dreamed the dreams of flasks. 30 dps increase.
Elixir of Major Frost Power (Battle) - +55 Frost Damage, same as above but frostier.
Greater Arcane Elixir (Battle) - Straight up +35 Spell Damage, good if you hate crit and want 11 more damage than Adept's.
Elixir of Mastery (Battle) - What? You can sustain 1500 dps but you only have 3k health? +15 stats for you then.
Elixir of Major Mageblood (Guardian) - Excellent choice to go with any of the battle elixirs. Obviously they had to bleed an Arc mage since it's +16mp5.
Elixir of Empowerment (Guardian) - Interesting elixir, though not very useful on raid bosses. Reduces targets resistances by 30.
Elixir of Major Fortitude (Guardian) - Not just for meat shields, quite useful if you need a little extra health. +250 health and 10 health per 5 seconds.
Elixir of Draenic Wisdom (Guardian) - +30 int/spirit, very good way to improve your mana bar while adding a bit of crit.
Oils persist through death and now last 1 hour and are a very effective way to boost your stats.
Superior Wizard Oil - By far the cheapest and easiest to obtain. +42 spell damage.
Superior Mana Oil - Alternative to wizard oil, +14mp5 for you wand spec'd mages.
Brilliant Wizard Oil - Pre-TBC oil, this version is in my opinion superior to Superior Wizard Oil though much more expensive and quite difficult to find. Requires Zandalar Tribe (ZG) - Honored to learn this recipe.+36 spell damage/+14 spell crit.
Foods are a great way to buff needed stats without hurting your gold sack. I'll list a few useful foods, but keep in mind there are several foods with different names that have the same effects.
Blackened Basilisk - 23 spell damage.
Crunchy Serpent - 23 spell damage.
Poached Bluefish - 23 spell damage.
Blackened Sporefish - 20 stamina and 8mp5.
Skullfish Soup - 20 spell crit.
Feltail Delight - 20 stamina.
Buzzard Bites - 20 stamina.
Spicy Crawdad - 30 stamina.
Fisherman's Feast - 30 stamina.
One is expected to carry a suitable amount of both Mana and Healing potions, but here I'll be listing some other things you can gulp down during raids.
Super Rejuvenation Potion - 1650 to 2750 Health AND Mana. Superior in almost every way to other healing/mana potions.
Major Dreamless Sleep Potion - My personal favorite, restores 3600 health and mana over 12 seconds. Sadly, it incapacitates you for those 12 seconds and can only be broken by damage, dispelling or waiting. Use with caution, as stunning yourself can be dangerous.
Fel Mana Potion - Restores 3200 mana over 24 seconds but reduces spell damage by 25 for 15 minutes. This debuff stacks up to 10 times and will persist through death.
Destruction Potion - Increases spell crit by 2% and spell damage by 120, uses your potion CD. Great for when you don't really need your CD and you most likely won't be taking any unexpected damage.
Flamecap - Not a potion, but it shares the mana gem/healthstone CD. +80 fire damage for 1 minute.
hmmm those all seem to be BC level 70 flasks/ELixirs and food.
The list is pretty short for WOTLK :
Flask of the Frostwyrm - +250 Spellpower for an hour, lasts through death.
Fish Feast, Or tender shoveltusk, or Spicy Salmon - all give 46 Spellpower for an hour.
The new Pilgrims Bounty has a "Bountiful feast" which works jsut like a fish feast, but gives 47 Spellpower. (It requires you to make a ton of the thanksgiving food, then combine them together to make a feast) and the Cranberry food also gives +47 spellpower but it only lasts a few days before it goes away.
I am not an alchemist, but I haven't found anything that is more useful for DPS then that flask and food combo. I am open to suggestions if anyone uses alternatives.