Stan Lee rocks an amazing set of Fantastic Four pajamas when Penny and Leonard come to visit him at his home unannounced.
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When Leonard goes to surprise Penny with a trip to Switzerland, he makes her a plate of Swiss hints.
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On the 3/1/10 episode of The Big Bang Theory, Sheldon ends up in jail. Don't worry. He'll get bailed out.
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This photo is taken from "The Einstein Approximation." During the half hour, Sheldon continues to search for the answer to a physics problem.
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After some security concerns after a break in, Sheldon finds himself sneaking out on his ledge.
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Penny and Leonard come outside to see Sheldon trapped by a net from the security system they installed.
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When Sheldon and Raj get a security system installed to combat intruders, it back fires on them.
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When the boys' apartment gets broken into, they call upon Wolowitz to help them install a security system.
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TBBT Quotes

Sheldon: I recently read that during World War Two, Joseph Stalin had a research program to create supersoldiers by having women impregnated by gorillas.
Howard: What a sick use of science.
Raj: Hey, as long as the baby's healthy.
Amy: I wonder if Stalin considered any other animals.
Leonard: Hippos are the deadliest creature. A half-human, half-hippo soldier would be pretty badass.
Howard: Yes, but when they're hungry-hungry, you can stop them with marbles.
Sheldon: Yeah, the correct animal for interspecies supersolider is koala. You would wind up with an army so cute it couldn't be attacked.

Raj: Well, to paraphrase Shakespeare: It's better to have loved and lost than to stay home every night and download increasingly shameful pornography.
Penny: Oh... you poor baby.
Raj: What's wrong with me, Penny?
Penny: Nothing, nothing. You know, if we weren't friends - and you hadn't brought up that creepy pornography story - I'd be on you like the speed of light squared on matter to make energy.
Raj: Hey, you totally got that right. E = MC squared.
Penny: I listen. I have no idea what it means, but I listen.