I've been a reader for a while now and i've got a lot of tips from you guys on this forum! I think it will be time for me to contribute in a small way at least, i hope someone finds this "guide" useful !

So, after rolling a new toon on a new server just before cataclysm to get a fresh start i decided to get Engineering + JC as my professions. Since it's a new toon i can't affoard the insane AH prices ( Copper 15g / stack, and up to 150g/ stack for fel iron). With nothing better to do before cata i decided to mine my way to engi + jc. This is not a complete guide, but it's what worked for me.

Mats List (This is a rough estimate of what you need to bring both JC and engi to max. Some people need more and some people need less, RNG skillups = win)

40 Rough Stone
320 Copper Bar
120 Tin Bar
20 Tigerseye or 20 Malachite
50 Weak Flux
15 Coarse Stone
29 Linen Cloth
240 Bronze Bar
60 Shadowgem OR 20 Shadowgem and 20 Small Lustrous Pear
35 Moss Agate [
120 Heavy Stone
80 Wool Cloth
20 Medium Leather
260 Solid Stone
301 Mithril Bar
25 Citrine
15 Truesilver Bar
5 Aquamarine
20 Mageweave Cloth
40 Dense Stone
242 Thorium Bar
10 Star Ruby
20 Large Opal
10 Powerful Mojo OR 10 Blue sapphire
10 Essence of Earth or 10 Essence of Undeath
20 Huge Emerald
20 Runecloth
95 Fel Iron bar
55 Green Gems OR 40 and 15 Black Diamond
20 Mote of Earth
10 Mote of Fire
50 Adamantite Bar
40 Adamantite Poweder (200 Adamantite Ore)
10 Primal Earth
30 Netherweave Cloth

Around 70 from any of the following gems: Bloodstone, Chalcedony, Dark Jade, Huge Citrine, Shadow Crystal, Sun Crystal. Make sure to get at least 5 Bloodstone, 1 Chalcedony, 1 Shadow Crystal and 1 Dark Jade, because you will need the Bloodstones when you reach 395 and the other gems when you reach 440.

284 Cobalt Bar
8 Frostweave Cloth
82 Crystallized Water
15 Crystallized Fire
10 Crystallized Earth
14 Borean Leather
9 Eternal Shadow
450 Saronite Bar
25 Skinning Knife
25 Mining Pick
25 Blacksmithing Hammer
13 Titanium Bar
5 Dream Shard
46 Eternal Earth OR 23 Eternal Earth and 23 Eternal Shadow
5 Forest Emerald
2 Eternal Fire
2 Eternal Water
2 Eternal Air
1 Frozen Orb
Around 28 Skyflare diamond OR 28 Earthsiege Diamond.

Where to mine (This is where i mined, and it worked very well for me)

Copper - Elwyn forest, i ran along the edges of the zone and each pass took about 12 min.

Tin - Northern Stranglethorn Vale, Around Kurzens Camp and inside the cave there.

Iron - Western Plaguelands, along the edges of the zone, each pass took a bit longer than in elwyn but there is one node where 5-7 deposits spawn on top of eachother (this will get fixed in the near future i suspect)

Mithril - Badlands, again alongside the edges of the zone but there is a lot of mithril here so passes here might take pretty long.

Thorium - Here you should make sure to check all the small caves especially the big one in the southeast end of the zone. There are a few rich deposits there.

Fel Iron - Hellfire Peninsula

Adamantite - Nagrand, make sure to check all the caves!

Cobalt - Zul'drak was the most effective choice for me, there is a lot of cobalt there.

Saronite - Icecrown will be the final stretch, the ore is scattered across the whole zone and if you're lucky you can get quite the ammount of rare ore here.