WoW Alchemy Leveling Guide 1 - 450
The following is an approximation of how many of each item it might require to level your alchemy from 1 to 450. The guide is here just as a reference as it will never be exactly the same every time you level. If you run out of mats and the auction house does not have any to buy, just look for another plan that will raise your level then continue the guide from there.
Gold is cheap, but your time is not!
Alchemy Materials:
59 x Peacebloom
59 x Silverleaf
80 x Briarthorn
30 x Bruiseweed
15 x Mageroyal
40 x Stranglekelp
30 x Liferoot
30 x Kingsblood
45 x Goldthorn
5 x Wild Steelbloom
70 x Sungrass
15 x Khadgar's Whisker
4 x Iron Bar
1 x Black Vitriol
4 x Purple Lotus
4 x Firebloom
19 x Arthas' Tears
40 x Blindweed
75 x Golden Sansam
40 x Mountain Silversage
38 x Felweed
20 x Ragveil
101 x Dreaming Glory
10 x Netherbloom
40 x Nightmare Vine
20 x Talandra's Rose
70 x Goldclover
41 x Tiger Lily
24 x Adder's Tongue
10 x Icethorn
40 x Lichbloom
10 x Dark Jade
10 x Huge Citrine
10 x Eternal Fire
74 x Empty Vial
65 x Leaded Vial
99 x Crystal Vial
170 x Imbued Vial
WoW Alchemy Guide 1-60
59 x Minor Healing Potions - 59 Peacebloom, 59 Sliverleaf, 59 Empty Vial (Save for later use)
WoW Alchemy Guide 60-110
50 x Lesser Healing Potion - 50 Minor Healing Potion, 50 Briarthorn (Sell)
WoW Alchemy Guide 110-140
30 x Healing Potion - 30 Bruiseweed, 30 Briarthorn, 30 Leaded Vial (Sell)
WoW Alchemy Guide 140-155
15 x Lesser Mana Potion - 15 Mageroyal, 15 Stranglekelp, 15 Empty Vial (Sell)
WoW Alchemy Guide 155-185
30 x Greater Healing Potion - 30 Liferoot, 30 Kingsblood, 30 Leaded Vial (Sell)
WoW Alchemy Guide 185-210
25 x Elixir of Agility - 25 Stranglekelp, 25 Goldthorn, 25 Leaded Vial (Sell)
WoW Alchemy Guide 210-215
5 x Elixir of Greater Defence - 5 Steelbloom, 5 Goldthorn, 5 Leaded (Sell)
WoW Alchemy Guide 215-230
15 x Superior Healing Potion - 15 Sungrass, 15 Khadgar's Whisker, 15 Crystal Vial (Sell)
WoW Alchemy Guide 230-231
1 x Philosopher's Stone - 4 Iron Bar, 1 Black Vitriol, 4 Purple Lotus, 4 Firebloom (Keep)
WoW Alchemy Guide 231-250
19 x Elixir of Detect Undead - 19 Arthas' Tears, 19 Crystal Vial (Sell)
WoW Alchemy Guide 250-265
15 x Elixir of Greater Agility - 15 Sungrass, 15 Goldthorn, 15 Crystal Vial (Sell)
WoW Alchemy Guide 265-285
20 x Superior Mana Potion - 40 Sungrass, 40 Blindweed, 20 Crystal Vial (Sell)
WoW Alchemy Guide 285-300
15 x Major Healing Potion - 30 Golden Sansam, 15 Mountain Silversage, 15 Crystal vial (Sell)
WoW Alchemy Guide 300-310
10 x Volatile Healing Potion - 10 Golden Sansam, 10 Felweed, 10 Imbued Vial (Sell)
WoW Alchemy Guide 310-325
15 x Elixir of Healing Power - 15 Golden Sansam, 15 Dreaming Glory, 15 Imbued Vial (Sell)
WoW Alchemy Guide 325-335
10 x Mad Alchemists's Potion - 20 Ragveil, 10 Crystal Vial (Sell)
WoW Alchemy Guide 335-340
5 x Super Healing Potion - 10 Netherbloom, 5 Felweed, 5 Imbued Vial (Sell)
WoW Alchemy Guide 340-360
20 x Super Mana Potion - 40 Dreaming Glory, 20 Felweed, 20 Imbued Vial (Sell)
WoW Alchemy Guide 360-365
5 x Icy Mana Potion - 10 Talandra's Rose, 5 Imbued Vial (Sell)
WoW Alchemy Guide 365-380
15 x Spellpower Elixir - 15 Goldclover, 15 Tiger Lily, 15 Imbued Vial (Sell)
WoW Alchemy Guide 380-385
5 x Potion of Nightmares - 5 Goldclover, 10 Talandra's Rose, 5 Imbued Vial (Sell)
WoW Alchemy Guide 385-395
10 x Elixir of Mighty Strength - 20 Tiger Lily, 10 Imbued Vial (Sell)
WoW Alchemy Guide 395-405
10 x Elixir of Mighty Agility - 20 Goldcover, 20 Adder's Tongue, 10 Imbued Vial (Sell)
WoW Alchemy Guide 405-410
5 x Runic Healing Potion - 5 Goldcover, 10 Icethorn, 5 Imbued Vial (Sell)
WoW Alchemy Guide 410-425
15x Runic Mana Potion - 15 Goldcover, 30 Lichbloom, 15 Imbued Vial (Sell)
WoW Alchemy Guide 425-435
10 x Transmute: Earthsiege Diamond - 10 Dark Jade, 10 Huge Citrine, 10 Eternal Fire (Sell)
WoW Alchemy Guide 435+
From here it's all up to you what you want to make as it gets really expensive and you can pretty much create any Alchemy potion you want.