Picturesque Views in England and Wales
The most admirable of his drawings, however were published in the 'England and Wales' volumes which the public have never appreciated as they deserved, chiefly because, during their progress, the application of steel induced a cheaper class of publications; of these the choicest, to the number of forty, are in the possession of Mr Windus.  The sceptics as to Turner will do well to examine them. We may see his paintings every year at the exhibition, but his drawings are known only through the engravers; no man loses so much by the transfer; to judge of one of them by the copy, would be almost like pronouncing an opinion on the nature of the ocean, from a sample bottle of salt water.
BG Windus was the owner of the largest single group of original watercolours from Turner’s Picturesque Views in England and Wales, the first main publication to include Turner’s work.  This series was the inspiration of the engraver and publisher Charles Heath who produced 96 engravings between 1827 and 1838.  They are considered among the finest British topographical engravings of the nineteenth century.
These are two examples from the publication – Salisbury and Saltash - which were in the Windus collection:
Saltash is the only dated watercolour in the whole series and so is thought to have been among the first group that Turner delivered to Charles Heath in February 1825.  The watercolour can be seen at the end of the lower right row in John Scarlett Davis’s watercolour of Windus’s Library.  However Ruskin was not impressed by this painting, referring to it in The Harbours of England (1856) as ‘an inferior work’.
William Robinson noted BG Windus had ‘Thirty-six Drawings made for the work designated Turner’s England and Wales, among them the beautiful Drawings of Okehampton, Donstanborough Castle, Yarmouth, Buckfastleigh, Tamerton, Hampton Court, Exeter, Dartmouth, Kilgarren Castle, Aldborough, Carew Castle, Holy Island. Windsor Castle, Dolbadern Castle, Saltash, Richmond Town (York), Fowey Harbour, Ditto (distant view), Malvern Abbey and Gate, Malmsbury Abbey, Folkestone, Cauldron Snout Fall (known as the Chain Bridge across the River Tees), Stoneyhurst, Lancaster, Alnwick Castle, Lancaster Lands, Devonport, Salisbury, West Cowes &c &c’

An additional note states that:
Mr. Windus is still adding to his Turner-collection, whenever any choice specimen can be obtained. Windermere Lake, Durham Cathedral, and Eaton [sic] College three very beautiful drawings, have been added since the previous account was printed. ​
The History and Antiquities of the Parish of Tottenham, in the County of Middlesex, 1840

Additional paintings have been identified more recently as: Boston, Tamworth Castle, Carisbrook Castle, Brinkburn Priory, Straits of Dover and Tynemouth.
Among the finest plates of the ‘England and Wales,’ of the castles may be mentioned Kilgarren, high above its dark woods and shining river; Windsor, steeped in afternoon sunshine; Kenilworth, wan and solitary at moonrise; Alnwick, massive and solemn beneath the full moon. Of the cathedrals, Durham, Ely, and Salisbury. Among English towns, Dudley, with its ancient, deserted castle high above the forges and chimneys which are pouring out their flames and smoke, vividly suggests, as Turner intended, the contrast between the departed feudal age and the rushing industrial life of to-day. How peaceful and beautiful are the ruins of Rievaulx, Valle-Crucis, Malmeshury, and Llanthony abbeys. For natural effects, notice the shining reaches of Winandermere, the rainbow on Keswick Lake, the sunny shores of Flint, the clear, fresh, evening sky and crescent moon of Cowes. For moorland grandeur, The Chain Bridge over the Tees cannot be surpassed, and no hand but Turner’s could have rendered the sweep and fury of storm and sea as in Lowestoffe, and the Longships Lighthouse. Is it too much to say that any one of these plates would have been sufficient to have made the fame of a landscape-painter?
W G Rawlinson The engraved work of JMW Turner RA Vol 1
Note: The paintings in bold were in the Windus Collection
According to the Tate:

Andrew Wilton has described the subjects ‘as modern “history pictures” in which the common man is the hero’ and certainly it is the relationship of man to the landscape which is the series’ constant theme. Unlike previous engraved series, Turner himself selected the subjects, which fall into a wide range of categories covering almost every aspect of his work as a landscape painter – coastal subjects, urban and industrial views, English pastoral scenes, and views of cathedrals and abbeys.  Many of the subjects were adapted from extant sketches or watercolours, although thirteen were based on new material gathered by him on a tour to the Midlands in 1830 undertaken especially for the project. In the variety and richness of its subject matter, and in the breadth and universality of its vision, Picturesque Views in England and Wales surpasses all the other series in which Turner had hitherto been involved. And the engravings are some of the most sophisticated and accomplished ever made after his designs.
The theme is one upon which the warmest enthusiasm would be justifiable; more exquisitely perfect productions never came from the pencil of a human being; they tempt us to picture the artist as in form the most graceful, in heart the most generous, in fancy the most brilliant, and in mind the most powerful of living men; for it seems impossible that one who is not all this, could have seen and pictures Nature so abundant in loveliness, and have made his own all that in her is most admirable.
Although Picturesque Views was seen as an artistic triumph, sadly it was a commercial failure.

Picturesque Views of England and Wales

Picturesque Views of the Southern Coast