The word collage derives from the original Greek word "koll" to stick, it is subsequently adopted/adapted into the French verb "coller" to stick. Interestingly, there is another meaning and that is the colloquial usage referring to an illicit liaison. As a consequence Francis Frascina  points out that "words and images cohabit, producing novel combinations and contexts".
Pablo Picasso was the first to introduce us to collage with his "Chair" which used plastic weaving for the seat and rope for the frame. Collage has moved on quite a lot since then and mainly adopts an abstract form. People like Malevich also produced collage in an abstract way with this Woman at the Poster Column, 1914.
Picasso subsequently produced collages using newsprint particularly from La Journal, the daily French newspaper. He would often cut the word to read La Jou which could imply a number of words/meanings, to aim at, to play, to enjoy and so on, and is indicative of Picasso's sense of humour. Picasso would also incorporate drawing skills in his collages, a practice which has been continually adopted by some artists to the present day. Picasso frequently used the image of a guitar in his work, which is the symbolic instrument of Spain. Whilst his method in using cardboard, paper, painted strips, sand etc., to achieve a cubist perception of the subject, his overall composition often forms a central position.
Victor Pasmore developed geometric shapes using card and gilding with positive and negative shapes, that were different from Picasso's collages. He also constructed neat abstracts, which are nearer to constructions than collage using wood perspect and card in a minimalist refined way. In his Gardens of Hammersmith, he used dried plant matter with a combination of paint to produce an attractive simple collage. His compositions generally do not occupy a central space but are often off-centre but well balanced, from collage he moved to constructions and he was involved in the design of the Peterlee Pavilion over water. He uses biomorphic forms in his abstract paintings, and are similar to Ben Nicholson's white low relief geometric work.
David Mach uses collage to product a semi-realistic painting with a surreal type of image, using pieces of paper almost like a mosaic. His work is on a huge scale and is frequently marine in subject matter though usually linked to a familiar London scene of either the Embankment, Canary Wharf, Harrods, the Dome. I remember seeing one of his works at a Summer Exhibition and being mesmerized by it, as there is so much detail to observe. The surreal element is not disturbing as, for example, de Chirico, but more like Dali in that the scenes are out of context with their surroundings, but are nonethless plausible artistically speaking.
Stephen Buckley has moved collage on so that it no longer sits on a rectangular or square support. In his latest work he has introduced a variety of shapes on which to produce his art and I feel this represents a significant change in the way that art is presented. He has an interest in heraldry and some of his work reflects that. He has a recurring motiff which appears to be a floral pattern stamp which he uses in different colours and various ways incorporating it to form a repeating pattern or randomly. He uses wood, card, canvas and rope. His work, Gloucester, refers to Shakespeare's character in Richard III and draws on Italian Rennaissance art, particularly Uccello. I can't see the connection myself, apart from the use of poles, which possibly echoes Uccello uses of lances in many of his epic battle paintings, which are also very decorative as well as being figurative.
Sandra Blow (1925-2006), produced some interesting collages, she used sawdust, sackcloth and plaster. She had connections with Cornwall in her earlier years and painted on a grand scale using pieces of coloured card and paint in her work, which is abstract and uses geometric shapes with strong flat colour, similar to the work of Matisse. During the 50s she was connected with artists such as Patrick Heron and Gilian Ayres. Her studio gives an indication of the scale of her work and has many boxes filled with various coloured card and paper.
Romare Bearden (1911 - 1988) uses many different materials including matte colored construction papers, pressure sensitive glossy
laminates, brightly printed commercial sheets called Color-Aid, and wall paper
and wrapping paper, as well as bright foils and patterned fabrics. His Afro-American roots are explored in the subject matter of his work. Bearden's collages are mainly colourful and are reminiscent of Matisse and also of Gauguin, particularly his Reclining Nude, which reminds me of Nevermore. His work is basically figurative and any attempts at a more abstract style generally do not quite work in my opinion, except for Now the Dove and the Leopard Wrestle, which is influenced by Picasso's Guernica.
 Frascina, Francis "Collage:Conceptual and Historical Overview"
Other References: Individual Websites of artists, National Gallery of Art, Tate (tate.org.uk), www.sites.si.edu, artsy.net