Victoriana.com has a picture of a "late Victorian men's hat, circa 1900":
http://www.victoriana.com/Mens-Clothing/mens-hats.html There are pictures of other styles at
http://www.gentlemansemporium.com/store/hats.php And victorianweb.org has a detailed description at
http://www.victorianweb.org/art/costume/nunn22.html :
"The tall silk or top hat continued for formal day and evening wear; the opera hat (gibus), covered in corded silk, also continued for visiting the theatre, as it could be folded flat and put under the seat. A light grey top hat was worn in the late 1860s for coaching or racing parties (and is still worn for Ascot Week in England). The bowler (Derby) named after its designer, the hatter William Bowler, worn from 1860, was a hard felt hat with a domed crown, varying in height over the years, and a narrow brim rolled up at the sides. At first, when worn with the loungejacket, it was black, but as its popularity increased it was also made in brown or fawn and teamed with the Norfolk jacket. A similar hat with a hard square crown was worn in the 1890s and much favoured by Winston Churchill, who continued to wear it into the 20th century.
"From the 1870s an increasing number of hats were considered suitable for informal wear. The Homburg, made fashionable by the Prince of Wales, was a stiff felt hat with a dent in the crown running from back to front, its brim bound with ribbon and curving up at the sides. The trilby, worn in the 1890s, had a similar dent in the crown but was softer with a wider, unbound brim. The wide-awake, a broad-brimmed felt hat with a lowish crown, was a, countryman's hat, but there are photographs of Alfred Tennyson looking extremely impressive in one in the 1850s. The boater, a stiff straw hat with a moderately deep, flat-topped crown encircled by a petersham ribbon and a flat narrow brim, was universally popular with men and women for the country, the seaside and boating; also worn by the seaside was the helmet, made of cloth with a small brim and a helmet-shaped sectional crown. Caps of tweed or firmly woven wool had small peaks and were quite close-fitting; the deer-stalker had a peak fore and aft and ear-flaps worn tied together on the top of the crown."