FIRST Design
by Jeff
Image text: Pool on the roof must've sprung a leak.
This comic is about a robot competition between two sides. The protagonist's side comes up with a robot that has a match on an extending arm to set off the sprinkler system to disable the opposing robot. Then the protagonists added an umbrella to their robot so that their robot could complete the competition without getting wet.
The image text is the protagonist's flimsy excuse for the reason there is water everywhere.
UPDATE: As Zero Cool and Alexandra said in the comments, the Image text is a reference to the movie, Hackers.
Stephen and Me
by Jeff
Image text: Hey, let go! We were all thinking it! Someone had to speak truth to power!
This comic is a parody of the movie/documentary by filmmaker Michael Moore called "Roger and Me" in which he detailed the problems that General Motors created in his hometown of Flint, Michigan by moving the manufacturing to Mexico. Roger is reference to General Motors CEO Roger Smith.
Stephen Odell is the CEO of Volvo, so the parody becomes "Stephen and Me".
The image text in this case is a continuation of the comic and what the filmmaker with the beret would say when he was being taken by security.
Silent Hammer
by Jeff
Image text: I bet he'll keep quiet for a couple weeks and then-- wait, did you nail a piece of scrap wood to my antique table a moment ago?
In this comic, we see the return of the Black Hat character, who this time is using his silent hammer invention for trouble. The skeptics society is a group based on the fact that they must apply reason to all situations and only supports claims that have compelling and complete evidence. Obviously, the Black Hat character knew this before puling this prank on the "Chair of the American Skeptics Society". There does not appear to be such a title in real life, but Michael Shermer is the Executive Director of the Skeptics Society.
Additionally, it is probably not a coincidence that the Black Hat character returns on comic number 666.
Listen to Yourself
by submission
Image Text: Man, I just wanted to know how babby was formed.
This explanation is by Harm. Harm is a reader of xkcd and explainxkcd. Harm writes explanations. Harm wrote that sentence mentioning that he writes explanations. Harm didn't write the previous sentence.
Here we see an interesting reversal as Black Hat observes Megan writing a virus to read back an author's post. Youtube is known for having commenters that say remarkably stupid things (for no apparent reason), and is previously mentioned in http://xkcd.com/301/. The twist here is that the commenter is shown to not realize how stupid their post is, and proceeds to sulk in shame...something that is unlikely to really happen.
The image text refers to a once-popular meme that originated from what is assumed to be a typo in a Yahoo! Answers post ("How is babby formed?"), which is later mentioned in http://xkcd.com/550/. A rephrasing of the question could be "How is a baby made?" The post was mocked rigorously, and the sentence was later used as a form of trolling. The image text implies that the original poster didn't intend for it to go memetic, and has their feelings hurt.
An interesting note is that Youtube has a feature for reading back posts to the writer, which may or may not have been because of this comic. (ed note: it was because of this comic.)