By way of introduction to these impressive shields in York Minster, here's a shot that includes a number of them which will give you an idea of what an impact they make in the cathedral.
Please feel free to click on the image above to see a larger, and thus more detailed photograph of these shields that will give you a better "feel" for them than you can get from just the picture here.
These coats of arm are,* from left to right:
William de Beauchamp, Earl of Warwick: Gules a fess between six crosses crosslet or;
Humphrey de Bohun, Earl of Hereford and Essex: Azure, a bend argent cotised or between six lions rampant or;
Aymer de Valence (1270-1324) or William de Valence (d. 1296), Earl of Pembroke: Barry argent and azure an orle of martlets gules;
Henry de Bolton, Lord Mayor of York 1335-1337): Or on a chevron gules three lions passant guardant or;
Ulf (a Danish thegn, or thane): attributed arms, Vert six lions rampant or); and
Margaret of France, the second wife of King Edward I: France ancient (Azure semy-de-lis or).
* Most of the sources that I have to help identify these shields give only the surname. I have tried to be more specific in the identifications in this (and following) posts, using primarily Aspilogia III: The Rolls of Arms of Edward I by Gerard J. Brault. Even then, though, in several cases, the arms could represent more than one individual; a father or his son, or one of two (or more) brothers. I have tried in these instances to make my best guess, or to include the individuals who are the likeliest candidates.