Works of art using the nipple or breast (in an unusual way, outside the standard nude or erotic context):

Dislocated:

• Sir Astley Paston, L'évolution du mamelon d'un sein féminin avec l'âge (1840): scientific sketch
• Janine Antoni, Wean (1989-90)
• Viktor Ivanovski, 311-11 (date?)
• Womanhouse installation: Robin Weltsch’s Kitchen and Vicki Hodgetts’s Eggs to Breasts (1972)
• Robert Gober, untitled (2000-1), untitled (1999), Untitled (detail) (2003-5)
• Nicola Costantino, Nipple Hermes handbags, Birkin and Kelly (2006)
• Szapocznikow Alina, Dessert II (Coupe de Seins)(1970-1)
• Margi Geerlinks, Young Lady I & II (2001)
• Louise Bourgeois, Nature Study (1984/2001)
• Ellen McMahon, Mama Do You Love Me (1996-7)
• Sarah Chuldenko, And Afterwards Things Grew Back a Bit Different (2008)
• Mickry 3, Get Physical: Silvie and Rebecca (2008)
• Ron English, Marilyn with Mickeys (2011)
• Linder Sterling, Untitled (1977)
• James Cabot Ewart, Nipples at the Met (wesite, 2012-present): Documents all the nipples at the Metropolitan Museum of Art.
• Sarah Lucas, Miss Jumbo Salavoy Situation (2012)
• Judy Fox, Lust (2007)
• John Bock, A gentleman works, when a gentleman works (film still) (2002)
• Nam June Paik with performer Charlotte Moorman, TV Bra for Living Sculpture (1969) (Youtube video)
• Annette Messager, La Ballade de Pinocchio à Beaubourg (detail) (2007)

Exaggerated/stylized/abstracted/idealized:

• Venus de Willendorf (24,000 B.C.E – 22,000 B.C.E.)
• Niki de Saint-Phalle, Black Venus (1967)
• Pablo Picasso, Girl with a Mandolin (Fanny Tellier) (1910): "If we look at the displacement of the representation of volumptuous, velvety substance from the nude's breast - the very form that should normally carry it - to the empty space behind the figure, we are forced to compare a site of carnal pleasure now become merely a flattened, jagged shape hung away from the body and a patch of 'empty' space now endowed with the qualities of detectability no longer imputed to the bodily form." Rosiland Krauss, The Motivation of the Sign.
• Jean Fouquet, Melun Diptych (circa. 1420–1477/81)
• Cindy Sherman, Untitled (1989)
• Eugène Delacroix, Liberty Leading the People (1830)
• Tom Wesselmann, Seascape #17 (1968)
• John Currin, The Bra Shop (1997), The Wizard (1994)
• Richard Phillips, Blessed Mother (2000)
• Lisa Yuskavage, Lupe & Lola II (2003)
• Takashi Murakami, 3-Meter Girl (2011), Hiropon (1997)
• Colin Christian, Bunny Sees Boobs! (2002)
• Vito Acconci, Adjustable Wall Bra (1990–91)
• Maurizio Cattelan, Stephanie Seymour (2003)
• Marc Quinn, Alison Lapper, The Fourth Plinth (2005-7)
• Allen Jones, Hatstand (1974)
• Richard Prince, Spiritual America (1983), untitled (girlfriend) (2000)
• Lynda Benglis, untitled ad submitted to Artforum (1974)
• Jenny Saville and Glenn Luchford, Four Works: Closed Contact A-D (2002): clearly inspired by Ana Mendieta's Untitled (Glass on Body Imprints) (1972)
• Barnaby Whitfield, Fit To Burst (Heather Stephens As The Bird Flu) (2007)
• Mel Ramos, You Get More Salami With Modigliani (1974)
• Thomas Hart Benton, The Rape of Persephone (1938-9)
• Sarah Hardacre, Gentlemanly Pleasures (2010)
• Matt Brown, Endocrine Series (2005)
• Terry Rodgers, Body of Knowledge (2004)
• Brenda Zlamany, Christina #2 (1994)
• Sue Williams, Shoes Take a Backseat (Green, Orange, and Blue) (1998)
• Hilo Chen, Beach 162 (2010)

Suckling:

• Afred Kubin, The Brood (1903)
• Patricia Piccinini, The Young Family (2005)
• Janine Antoni, 2038 (2000)
• Margi Geerlinks, Mothers (2000)
• Lucian Freud, Large Interior, Notting Hill (detail) (1998): originally the suckling figure in the background was a female model, but he later changed it to a male. Freud himself was gay, in fact he was the painter Francis Bacon's lover at one point. Lucian Freud was also Sigmund Freud's grandson, and we all know what the great psychoanalyst had to say about sexuality and gender.
• Catherine Opie, Self-Portrait/Nursing (2004)
• Kara Walker, The End of Uncle Tom and the Grand Allegorical Tableau of Eva in Heaven (detail) (1995)

Performance + other:

• Valie Export, Touch Cinema (1968-1971)
• Yoko Ono, Cut Piece (1964)
• Marina Abramović, Rhythm 0 (1974), Balkan Erotic Epic (detail) (2005)
• Martha Wilson, Breast Forms Permutated (1972)
• Hannah Wilke, S.O.S.Starification Object Series (1974-82)
• Cindy Sherman, Untitled (1989)
• Pierre Molinier, Travesti (with corset and nylons), manipulated self portrait (1969)
• Anna Anthropy, Dys4ia (2012): video game about the dysphoric feeling after a transexual sex reassignment surgery.
• Zefrey Throwell, Ocularpation: Wall Street Personal Assistant (2011)
• Bettina Rheims, VEROUSHKA KNOGE, ÉTUDE (2005)

This site collects a seemingly endless number of entries on breasts in art, and surprisingly, despite its crass title and topic, it displays some decent works of art, including many in the list above. Though, it seems to lack a lot of the feminist artworks.