Favorite cameo on Big Bang Theory?

Which of these cameos (scientist or not) is your favorite?
Poll suggested by yrnej

Discuss Here.
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1.
Summer Glau
Actress, Serenity
Summer is a native of San Antonio, Texas. She's been a ballerina most of her life. Her debut was in various commercials and a guest appearance on the WB's Angel. She has gone on to star on the TV series Firefly as well as its follow-up movie Serenity and the TV series Terminator: The Sarah Connor Chronicles.
 
2.
Wil Wheaton
Wil Wheaton was born Richard William Wheaton III on July 29, 1972 in Burbank, California. He first gained international attention by starring in the Rob Reiner comedy-drama film Stand by Me. He then played Wesley Crusher on the television series Star Trek: The Next Generation for three and one-quarter seasons...
 
4.
George Takei
Although primarily known for playing Hikaru Sulu in the television series Star Trek and the first six features, George Takei has had a varied career acting in television, feature films, live theater and radio. He also is a successful writer and community activist. George Takei was born Hosato Takei on April 20...
 
6.
Charlie Sheen
Charlie Sheen was born Carlos Irwin Estévez on September 3, 1965, in New York City. His father, actor Martin Sheen (born Ramon Antonio Gerard Estevez), was at the time just breaking into the business, with performances on Broadway. His mother, Janet Sheen (née Templeton), was a former New York art student who had met Charlie's father right after he had moved to Manhattan...
 
7.
“ "With all due respect, Dr. Cooper, are you on crack?" ” - dan_dassow
 
9.
Stan Lee
Writer, Iron Man
 
12.
Brian Austin Green
Brian Green was born on July 15th 1973 in Van Nuys, California to parents Joyce and George L. Green. He has a brother Keith and sister Lorelei. Brian's father was a Country & Western artist and used to frequently take him along to gigs and soon got him interested in the world of music. His first full-time...
 
13.
Brent Spiner
Brent Spiner, whose primary claim to fame is his portrayal of the beloved android Data on the television series Star Trek: The Next Generation, was born and raised in Houston, Texas. His parents, Sylvia (Schwartz) and Jack Spiner, owned and operated a furniture store, and were both from Jewish immigrant families (from Austria...
 
15.
 
17.
Leonard Nimoy
Actor, Star Trek
Leonard Simon Nimoy was born in Boston, Massachusetts, to Dora (Spinner) and Max Nimoy, who owned a barbershop. His parents were Ukrainian Jewish immigrants. Raised in a tenement and acting in community theaters since age eight, Nimoy did not make his Hollywood debut until he was 20, with a bit part in Queen for a Day and another as a ballplayer in the perennial Rhubarb...