Considering that, at least for me and many others that I'm aware of, the crafting process is most slowed by the hard to find "fine" crafting materials. Because of this, I figured it would be good to start a post on what drops which items, and where to go to get them. I'll start off with the little bit that I know myself, and update the sections as we find more farming spots. If you know of a good spot, please post and I will try to keep this thread updated.
First, lets just get the fact that all crafting materials, fine or otherwise, can be found in loot bags out of the way. Loot bags are things like "Stolen Goods," "Ritual Bags," etc that you have to double click to get what's inside of. Loot bags drop off of pretty much everything that's remotely humanoid, such as Bandits/Pirates, Charr, Centaurs, Ettins, Trolls, Harpies, etc.
Also, crafting materials are based on a tier system, and which tier drops is based on enemy level. Your best bet to find a crafting material of a certain tier is to go to an area that is in that tier's level range. Some areas will actually cover two tiers, so you'll have to pay attention to the level of the enemies you're fighting to make sure you're getting what you want. I may be wrong about level ranges for each tier, but it seems to move in about 15-level increments from what I've seen so far. So Tier 1 is levels 1-15, Tier 2 is 15-30, etc. It's much the same way that the map areas are split up.
Now, on to the mats themselves -
Blood - Skales, Skelks, Bats, Harpies, and Trolls.
Tier 1(Vial of Weak Blood) - In Queensdale, just south of the Scaver WP there's an area with Ridgeback Skales.
Tier 2(Vial of Thin Blood) - Snowden Drifts, Darkhoof Hills. There's harpies to the west of the centaur camp and trolls to the east. Just watch out for the Champion troll.
-- Kessex Hills, Manfire Hills, skales
-- Gendarran Fields, Lake Gendarr, skales
Tier 3(Vial on Blood) - Fields of Ruin, Tanglerot Hills. Kill the harpies.
-- Blazeridge Steppes, Twin Sisters Crossing, Kill scales.
-- Harathi Hinterlands, Arca Lake, Kill harpies
Tier 4(Vial of Thick Blood) - Iron Marches, Ebbing Heart Run, Kill scales
Totems - Norn, Grawl, Jotun
Tier 2(Small Totem) - Snowden Drifts, The Frozen Sweeps WP. Sons of Svanir there drop them occasionally, but there's also lots of wolves and elementals that drop claws, so it's a general farm spot.
--Diessa Plateau, Holystone Caves - Kill the Grawl.
Tier 3(Totem) - Dredgehaunt Cliffs, Panther Snarl Shrine, Sons of Svanir
Dust - Ghosts, Undead, Elementals, "Branded" enemies.
Tier 1(Glittering Dust) - Plains of Ashford, pretty much anywhere ghosts are to be found there. The ghosts spawn pretty rapidly.
Tier 2(Shimmering Dust) - Diessa Plateau, Breached Wall, Kill ghosts. Again, they spawn pretty quickly here.
-- Gendarran Fields, Lawen Ponds, Kill risen.
Tier 3(Radiant Dust) - Fields of Ruin, head to the NW corner, and start killing everything.
Scales - Drakes, Fish, Skales, pretty much anything aquatic. Also can drop off of Devourers
Tier 1(Tiny Scale) - Calcedon Forest, Ruins of the Unseen, kill skritt
Tier 2(Small Scale) - Gendarran Fields, Lake Gendarr, kill barracuda.
-- Harathi Hinterlands, Guardian Lake, kill river drakes.
Tier 3(Scale) - Harathi Hinterlands, Arca Lake, kill barracuda.
Bones - Undead, Ettins, Trolls, Jotun, Grawl
Tier 2(Bone Shard) - Diesssa Plateau, Holystone Caves. Kill the Grawl.
Fangs - Bears, Warthogs, Plains Wurms, and Skelks.
Tier 2(Small Fang) - Diessa Plateau, Holystone Caves. Farm the grubs.
Claws - Charr, Raptors, Wolves, Drakes, and I think Devourers as well.
Tier 2(Small Claw) - Snowden Drifts, The Frozen Sweeps WP. The Icebrood Elementals and the Icebrood Wolves.
Venom Sacs - Spiders, Plains Wurms, Devourers, Grubs, and Wasps.
Tier 1(Tiny Venom Sac) - Queensdale, Shaemor fields, spiders
Tier 2(Small Venom Sac) - Brisban Wildlands, West of Ultra Metamagical's WP. Just farm the Breeze Riders.
-- Diessa Plateau, Holystone Caves. Farm the grubs.
-- Gendarran Fields, Overlook Cavern, cave spiders.
EDIT: Thanks Wolfenswan for that link, and thanks to all the people at GWG who have contributed to that thread. I'll add the stuff that I know sure should drop directly, but some of the stuff they mention looks like they might be listing drops received from loot bags. If anyone confirms a direct drop, or we find out that certain loot bags are better for certain things, I'll add them in.