Some of the variety of styles of heraldic surcoats, tabards, jupons, and cote-armors worn by men in the Middle Ages. These are worn over armor, and are most often seen (iconographically speaking) in tournaments, though they do appear in battle from time to time as well (though how often they're used as artistic shorthand to identify the characters, I don't know for sure). These do not appear as an overgarment in non-armored contexts. This list only includes the surcoats with armorial decorations; there are plenty more that are solid-colored or with non-armorial decoration (i.e., fancy brocade patterns, etc.)

These are different from livery coats, which would be worn in battle by those fighting for a specific person. These also seem to be different in construction from heralds’ tabards.

For more information on design and construction, see Tournament Costume, and these links. I'd also recommend reading Janet Arnold's “The Jupon or Coat-Armour of the Black Prince in Canterbury Cathedral” in the 1993 Journal of the Church Monument Society, and also The Interrelationships of Costume and Armor (The Metropolitan Museum of Art Bulletin).

• Several illustrations in Histoire d’Outremer, (British Library Yates Thompson 12), c. 1232-1261
• A knight making a gesture of homage, The Westminster Psalter (British Library Royal 2 A XXII, fol. 220), c. 1250
• Wall-painting at the Church of St. Cyriacus, c. 1250
• Saint-Bertrand-de-Comminges Knight, c. 1300
• Helain asks Gawain to have him made a knight, Lancelot Cycle (Ashmole 828, fol. 96v), beginning of the 14th century
• Fols. 80r, 86r, 95v, 96r, the Maastricht Hours (Brit. Lib. Stowe 17), 1st quarter of the 14th century
• Der Herzog von Anhalt (fol. 17r), Herzog Johann von Brabant (fol. 18r), Graf Friedrich von Leiningen (fol. 26r), Graf Albrecht von Heigerloch (fol. 42r), Graf Wernher von Homberg (fol. 43v), Herr Walther von Klingen (fol. 52r), Herr Heinrich von Frauenberg (fol. 61v), Herr Hiltbold von Schwangau (fol. 146r), Herr Walther von Metze (fol. 166v), Herr Hartmann von Aue (fol. 184v), Herr Goesli von Ehenheim (fol. 197v), Der von Wildonie (fol. 201r), Winli (fol. 231r), Herr Ulrich von Lichtenstein (fol. 237r), and Der Püller (fol. 253v) The Manesse Codex (UBH Cod. Pal. germ. 848), c. 1300-1330
• Fols. 81v, 82r, 83r, 85r, 85v, 86v, 87r, 88r in the Smithfield Decretals (Brit. Lib. Royal 10 E IV), c. 1300-1340
• Sir Robert Septvans, d. 1304 (or Sir William de Septvans, d. 1323)
• Lambert d’Abée and his wife, 1312
• King Eric Menved, d. 1319
• Marginal illustration, possibly St. George (fol. 39v) and Sir Geoffrey Luttrell (fol. 202v), the Luttrell Psalter (Brit. Lib. Add. 42130), c. 1325-1340
• Battle of the Catalaunian plains, Spieghel Historiael (KB KA 20, fol. 146v), c. 1325-1335
• Chroniques de France ou de Saint Denis (British Library Royal 16 G VI), second quarter of the 14th century
• Guidoriccio da Fogliano by Simone Martini, 1328
• Stonham Aspal knight, 1330
• Knight of Prato, Address to Robert of Anjou, King of Naples, from the town of Prato (British Library Royal 6 E IX, fol. 24), c. 1335-1340
• Several of the illustrations in The Romance of Alexander (Bodley 264), c. 1338-1344, including fols. 21v, 43v, and 51v. Fol. 67r shows an interesting detail of side-lacing, which we also see on some funeral effigies (like Nicholas de la Beche, John de Lyons, and John Leverick/the Ash knight).
• Sir Hugh Hastings (and weepers, including Amalric St Amand, Edward III, Henry Plantagenet, Ralph Stafford, Roger Grey, and Thomas Beauchamp), d. 1347
• The martyrdom of Thomas of Beckett in an English book of hours (Walters W.105.14R), 14th century
• Henry Plantagenet, Earl of Lancaster, 1340
• Ralph, Lord Stafford, d. 1347
• King William I (British Library Cotton Claudius D. II, fol. 33), 14th century
• Graf Gerhard I von Jülich and his wife (detail)
• John Foljambe, 1358
• Sir Peter de Grandison, 1358
• William de Aldeburgh, d. 1360
• William Disney, d. 1360
• Reginald Cobham, d. 1361
• Bernabo Visconti, 1363
• Sir Adam de Clyfton, 1367
• Thomas Beauchamp, d. 1369
• The tomb-effigy and jupon of the Black Prince, d. 1376
• Edward III and the Black Prince, 14th century
• Richard Fitzalan, 1376
• Hüglin von Schöneck, d. 1377
• Guillaume de Beauvais, 1380
• Many in BNF Fr. 343 (a manuscript with several Arthurian stories), c. 1380-1385, including Galahad's oath (fol. 7), Departure for the Quest of the Holy Grail (fol. 8v), Galahad (fol. 12), Meliant of Denmark loses the crown (fol. 14), Gawain with Lancelot and Percival (fol. 17v), Gawain (fol. 17), Lancelot (fol. 18), Percival (fol. 21v), Percival (fol. 27v), Percival (fol. 29)
• St. George, The Golden Legend (British Library Royal 19 B XVII, fol. 109), 1382
• Sir John Harsyck, c. 1384
• Edward III (British Library Cotton Nero D. VI, fol. 4), c. 1386-1399
• Guillaume de Voisins, 1394
• Hughes de Roucy, 1395
• Sir George Felbrigge, d. 1400
• Sir John Wingfield, c. 1400
• Sir Robert Marmion, c. 1400
• Thomas Beauchamp, 12th Earl of Warwick, 1401
• Richard II knighting Henry of Monmouth, Histoire du Roy d'Angleterre Richard II (British Library Harley 1319, fol. 5), c. 1401-1405
• Louis de Bourbon, 1404
• Sir William Bagot, d. 1407
• Sir Edmund de Thorpe, d. 1417
• Hero and Heroine, a fresco at La Manta Castle, c. 1420
• John Wantele, d. 1424
• Marguerite d'Orléans at a tournament, The Book of Hours of Marguerite d'Orléans (BNF Latin 1156 B, fol. 160), c. 1426
• The Battle of Crécy, Froissart's Chronicles (BNF Fr. 2675, fol. 150), second quarter of the 15th century
• William Bruges's Garter Book (British Library Stowe 594), c. 1430-1440
• The king of France in the Decameron (BNF Arsenal 5070, fol. 76v), 1432
• The king of Portugal dressed for a joust, c. 1433
• John Fitzalan, Earl of Arundel, d. 1435
• Virgin and Child with Jean Comte de Dunois, The Dunois Hours (British Library Yates Thompson 3, fol. 22v), c. 1440-1450
• Sir Thomas Holme’s Book of Arms (British Library Harley 4205): Part 1 (anonymous verses on the kings of England, to Henry VI) c. 1445-1450; Part 2 (Military Roll of Arms) c. 1446-1448; Part 3 (Legh's Men of Arms) last quarter of the 15th century or 1st quarter of the 16th century
• Challenge of Philip Boyle to John Astley (fol. 277v), Ordonances of Chivalry (PML M.775), c. 1449-1461
• The investiture of Alan of Brittany as Earl of Richmond by William the Conqueror (fol. 6v) and the Earl of Richmond with other knights (fol. 7r), Register of the Honour of Richmond (Lyell 22), second half of the 15th century
• Simon de Varie kneeling in prayer, The Hours of Simon de Varie (Getty MS. 7, fol. 2), 1455
• Cassone with a tournament scene, c. 1455-1465
• Battle, Hesperides (Canon. Class. Lat. 81, fol. 27r), c. 1457-1468
• Richard II goes to Ireland, Froissart’s Chronicles (British Library MS Harley 4380, fol. 166v), 1470-1475
• Sir John Say, d. 1478
• The Tournament-Book of René d'Anjou; use Mandragore to find Français 2692, Français 2693, or Français 2695.
• Sir Thomas Holme’s Book of Arms (British Library Harley 4205), c. 1482-1494 or early 16th century
• Jehan Chabot kneeling before Henry VII, Le Regime de Santé (British Library Royal 19 A. V, fol. 1v), c. 1485
• William de Grey, d. 1494/5
• Iolante at the tournament, The King's Three Sons (British Library Harley 326, fol. 113), c. 1500
• Charlemagne, c. 1500
• Several images in the founder's and benefactors' book of Tewkesbury abbey (Top. Glouc. d. 2, fol. 25v), beginning of the 16th century
• Drawing of the effigy of Edward Sutton, Lord Dudley, Wriothesley Heraldic Collections (British Library Add. 45131, fol. 92), early 16th century
• Olivier de la Chapelle, d. 1508/9
• Arnold of Louvain in The Gift of Kalmthout by Goswijn van der Weyden, 1511
• Hugh Wylloughbye, 1513
• Walter Curson, d. 1527
• Sir Richard Fitz-Lewes, 1528
• Sir John Clerk, d. 1539
• Jan Lopez Gallo and his three sons by Pieter Pourbus, 1568
• Portrait of a knight, 16th century (?)
• Tabard at Muiderslot