This will be a continued work in progress for obvious reasons.
Pendraken (UK) - 100% devoted to 10mm, massive selection of great minis, both historical as well as fantasy.
Magister Millitum (UK) - Historicals and fantasy alike, pretty reasonable price and quality.
Kallistra (UK) - Same miniatures sold by Pendraken but, from what I read, on the bigger side, they are also sold in strips instead of individual minis.
Copplestone Castings (UK) - Heavily inspired Middle Earthy, Mark Copplestone brought us, a fantastic, albeit limited, range with a tons of detail. Sold through Northstar Figures.
Old Glory (US) - Historical miniatures, with some being easily used as fantasy miniatures. Also available in the UK at OldGloryUk.
Eureka Miniatures (AU) - Mostly focused on recreating Warhammer armies that didn't had a Warmaster oficial release, fantastic detail and also available in the UK at Fighting 15s.
Rebel Minis (Mighty Armies range) (US) - Ocs and Wood Elf, sold as a ready made army.
Polar Fox Miniatures (RU) - Source of, fantastically sculpted, Warhammer themed Orcs & Goblins and Tomb Kings.
Warmonger Miniatures (US) - Small, but solid, Landsknechte range.
Trolls Under the Bridge (CZ) - Chaos warriors and chaos heroes.
Vanguard Miniatures (UK) - Warhammer inspirired Ogre Warriors.
Bestial Wars (US) - Very colorful wood elfs, treeants and abominations.
Warrior Miniatures (UK) - Small range of incredibly cheap but low detail historicals and fantasy miniatures.
Irregular Miniatures (UK) - Cheap with varying degrees of quality, good historicals.
Castle Arts (IT) - Pretty vast range of samurais and other Japanese related minis.
TB Line (IT) -Nice and solid range of medieval miniatures. Now sold by Pendraken.
New Line Designs (UK) - Good range of historical ancients.
ObeliskMiniatures (DE)- Small range of Conquistadores and Incas.
Laran Miniatures (UK) - A nice contingent of chaos warriors, skaven and empire, funded on indiegogo.com
Spellcrow (PL) - Expertly sculpted barbarians, lizardmen and dwarfs.
Black Gate Miniatures (UK) - Crowdfunded Ogres
Cibos Little Dudes (CH) - Amazing sculpts with a large offering.
Upcoming
10mm Fantasy Miniatures (??) - Upcoming skaven, chaos dwarfs and ogre range.
Out of production
Games Workshop (UK) - Their warmaster line had amazing detail and can still be found on ebay.
Game Figures, Inc. (US) - Used to produce the Minifig range, with a lot of fantasy miniatures, they also owned the A.I.M. range, filled with good quality samurai. Division After Division seems to be the new owners of the A.I.M. range but I couldn't find anything on them.
Tajima1 (UK) - A tiny range of chaos warriors that looked really good.
Evil Men - Yet another small contingent of chaos warriors, unfortunately no longer available. (See Laran Miniatures)
Ralpartha Europe (UK) - Great quality Warhammer inspired sculpts on their Demonworld range, use the monsters and spirits.
Magister Millitum (UK) - Great miniatures from their own Blood Dawn Fantasy range, their Orcs work really well as Ogres
15mm.co.uk (UK) - Classic fantasy sculpts with really nice monsters.
Khurasan Miniatures (US) - In my opinion, one of the best 15mm out there, not only in quality but also variety.
10mm Fantasy Miniatures (??) - Upcoming skaven, chaos dwarfs and ogre range.
Out of production
Games Workshop (UK) - Their warmaster line had amazing detail and can still be found on ebay.
Game Figures, Inc. (US) - Used to produce the Minifig range, with a lot of fantasy miniatures, they also owned the A.I.M. range, filled with good quality samurai. Division After Division seems to be the new owners of the A.I.M. range but I couldn't find anything on them.
Tajima1 (UK) - A tiny range of chaos warriors that looked really good.
15mm miniatures that work with 10mm
While a lot of 10mm manufacturers produce large infantry, you may find that 15mm manufacturers match the use and are usually cheaper. They are also a good source of monsters.Ralpartha Europe (UK) - Great quality Warhammer inspired sculpts on their Demonworld range, use the monsters and spirits.
Magister Millitum (UK) - Great miniatures from their own Blood Dawn Fantasy range, their Orcs work really well as Ogres
15mm.co.uk (UK) - Classic fantasy sculpts with really nice monsters.
Khurasan Miniatures (US) - In my opinion, one of the best 15mm out there, not only in quality but also variety.