I wanted to write a little about useful manuscripts for costume research/inspiration for the 1300s. There are, of course, a few well known favourites (like, say, the Luttrell Psalter). Luckily, more and more libraries are putting high quality facsimiles of their manuscripts on the web. The issue is, of course, finding them - often they are not terribly well publicised and, as an amateur, one often does not even know which manuscripts will be useful for your project, never mind which museum or library currently owns them.
So, I present to you a run-down of the useful illustrated manuscripts I have come across and where to find them. This list is liable to be updated from time to time - it's as much a reference for myself as for others!
Luttrell Psalter (British Library Add. MS. 42130, f.171)
Dated c. 1320-1340; Lincolnshire, England. Famous for its illustrations of the life of the rural poor. Also, a couple of illustrations of richer individuals. This has finally been completely digitised!
Le Roman de la Rose (University of Chicago Library MS. 1380)
This copy is dated c. 1365; France. Lots of illustrations of courtly men and women, a couple of illustrations of armoured men, a couple of illustrations of poor men and women.
Le Jeu des échecs moralisé (University of Chicago Library MS. 392)
Dated c. 1365; France; originally bound together with University of Chicago Library MS. 1380. A few images of courtly men and women, a fair few images of armoured men.
Romance of Alexander (MS. Bodl. 264)
This copy is dated c. 1338-1344; Flemish. Plenty of illustrations of courtly men and women, and of armoured men. One notable feature is the detail afforded to the clothing - unlike nearly all other Northern European pictures of this era, the clothes are depicted as being decorated with embroidery or patterned cloths, not simply plain. A higher resolution copy is available here.
Manesse Codex (Cod. Pal. Germ. 848)
Dated c. 1304-1340, with the majority of the illustrations completed c. 1304; created in Zurich. Full of images of knights (often jousting) and ladies (often watching the joust). There are 137 full-page images, each dedicated to a singer (plus one additional image that has been unassigned).
Maciejowski Bible, aka Morgan Bible (Morgan M. 638)
Dated c. 1250; France. Illustrated bible, famous for its highly detailed battle scenes.
Bible Historiale (Den Haag, MMW, 10 B 23)
This copy is dated c. 1372; France. Illustrated 'history bible'. Mostly illustrations of men and armoured men, some illustrations of women.
Chroniques de France ou de St Denis (BL MS Royal 20 C vii)
This copy is dated c. 1380-1400; France. Illustrated history of France. Plenty of illustrations of armoured men. Interesting for its illustrations of coloured coat armour and of furniture (being looted).
Chroniques de France ou de St Denis (BL MS Royal 16 G vi)
This copy is dated after 1332 but before 1350; France. Illustrated history of France. Plenty of illustrations of armoured and civilian men. F. 64 ('witches burnt') is intriguing, for its depiction of women in their shifts.
Très Riches Heures du Duc de Berry (Chantilly, Musée Condé, MS 65)
Dated 1412-1416 (Limburg brothers' illustrations) with some illustrations completed or added 1485-1489 (by Jean Colombe). Illustrated book of hours. Includes full-page illustrations for the months of the year which are highly popular with amateur costumiers for their depictions of early 15th C women's clothing (though it should be noted that these are not paintings of real life, but are composed scenes as requested by the patron - thus, though they are naturalistic they are not necessarily completely realistic).
Useful to view in conjuction with this website which has vastly inferior copies of the illustrations but has (occasionally slightly dubious) written descriptions/interpretations of each image and notes which illustrator worked on which page.
Roman de la Rose Digital Library
This incredible site has listed every single (known) extant copy of La Roman de la Rose and fragment copies - and, in many cases, there are links to online facsimiles. The only slight issue is the often broad datespans ascribed to the manuscripts which can make it difficult to form coherent timelines for the fashion. This is made up for by the ability to search by illustration title which enables one to analyse how depictions of allegorical figures, such as 'Vanity', changed with time.
Europeana Regia manuscript collection
A page with links to masses of full digitised manuscript facsimiles, searchable (among other things) by date. Wonderful. I have only taken a cursory look through currently.
French manuscripts 1300-1400 and Dutch manuscripts 1330-1430
Two more pages I have yet to fully explore. These are from the Museum Meermanno in the Netherlands.
Manuscripts from the Werttemberg State Library, Stuttgart
Yet more manuscripts I have not investigated.