The roots of assemblage can be traced back to early twentieth-century European collage, and a wide variety of artists have and do assemble their art work. Here is a partial list:

John Baldessari: Biography, Specimen (After Durer), Still Life: Choosing and Arranging (a virtual assemblage)

George Braque's Collages: Biography, Images

Joseph Cornell's boxes: WebMuseum, Paris, Introduction

Jean Dubuffet: Biography, Will to Power, The Soul of Morvan

Marcel Duchamp's Readymades: Marcel Duchamp World Community, ArtLex Readymade

Fluxus Movement: Fluxus Portal, Fluxus List, Manifesto, Life in Fluxus, Joseph Bueys, George Maciunas

Yuri Kuper: Tulip

Louise Nevelson: Biography, Museums and Galleries, Ancient City, White Column (from "Dawn's Wedding Feast"), Rain Garden II

Nam Jun Paik: Art in Context Library, Video Sculptures

Pablo Picasso's Famous Collage: Still Life With Chair Caning

Robert Rauchenberg's Combines: Monogram, PBS.org American Masters, at the Guggenheim, John Haber review

Betye Saar: ArtScene article by Marge Bulmer: Betye Saar, Princeton Online

Kurt Schwitters: CollageGallery Retrospective, Maraak, Variation I (Merzbild)

Dada and Surrealist Movements: ArtArchive essay, Max Ernst, Man Ray's Object to Be Destroyed (Indestructible Object)

Pop Art: Excerpt from Pop Art: A Continuing History, by Marco Livingstone

PostModernism and Art: John Haber's Art Reviews, Duchamp - book review

The Liberation of Aunt Jemima. Betty Saar,
1972. Mixed media, 12 x 8 x 3 inches. University of California, Berkeley.

Joseph Cornell, Untitled (Medici Prince)
c. 1953. National Gallery of Art.

Man Ray (American, 1890-1976), Objet indestructible (Indestructible Object),  1923/1965.
Metronome with photograph.
8 ½ x 4 ½ x 4 ½ in.