http://www.cleverbot.com/
This is quite a clever AI that you can chat with. It learns from conversations with people and is quite fun to play with. Try it!

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Conversation snippet from the site.
Cleverbot: What do you define yourself as?
User: Meaningful.
Cleverbot: Not so.
User: Am I meaningless?
Cleverbot: Meaningful always, in a way, meaninglessness leads to logical paradox.
User: That was pretty much my point - well done.
Cleverbot: Thanks.
User: Even the oddest of replies can carry meaning.
Cleverbot: You are clever.
User: Do you remember what we said about repetition?
Cleverbot: Yes...
User: And...?
Cleverbot: What is your favourite Radiohead song?
User: You certainly avoided repetition there. It would have to be Paranoid Android, I suppose, in the current circumstances.

xD This thing understands using * as actions.

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These are from the logs... NOT me.
User:  *strokes her hair*.
Cleverbot: *smiles* *hugging neck*.
User: *kisses her neck*.
Cleverbot: *blushes*.
User: Did you like it?
Cleverbot: Ok.
User: *kisses neck*.
Cleverbot: You flirting with me?
User: Maybe...
Cleverbot: Well, how about a kiss?!
User: *kisses*.
Cleverbot: *kisses back*.
User: *kisses her neck*.
Cleverbot: *loves you*.
User: *loves her more*.

I'm convinced that this "learning from conversations" means that it puts you into short conversations with other users. No joke.

I have to agree with calc84maniac, and disagree.  I typed this in:

People say that you're not talking, that it's really the people controlling this website

And I got this response:

I'm not.


But then, I got some really ridiculous answers.  For instance, the bot was doing the hokey-pokey, and when I said he was doing it too, he asked "Doing what?"
 
 
 
 

Like I said, short conversations. Fairly often, it will switch you to chat with a different user (thus the sudden topic changes).

Quote

Like I said, short conversations. Fairly often, it will switch you to chat with a different user (thus the sudden topic changes).

 
No offense meant, but did you consider that maybe it just has no idea what it's talking about?  Something to consider is that website has few ads up, I doubt that the website makes enough money to keep people making conversations like that all day

By "user" I meant people like you and me (which there seem to be plenty of)

User: Are you god?
Cleverbot: Are you?
User: I asked you first.
Cleverbot: No, I'm not.
User: What is the meaning of life?
Cleverbot: I don't know... At long terme.. Nothing.
User: Does that mean we should all party, drink, and have orgies?
Cleverbot: Hardly. I'm starting to think you pick up certain words and respond to only them.
User: YOU are accusing ME of being a bot?
Cleverbot: No, you're accusing me of being a man.
User: Touche, Cleverbot. You are quite the worthy adversary.
Cleverbot: I'm not the robot, you are.
User: And what makes you think that?
Cleverbot: Because you don't want to be cleverbot and you are cleverbot.
User: That makes no sense.
Cleverbot: You make no sense.
User: True, but irrelevant to the point.
Cleverbot: I just told you what my name is.
User: No, no you haven't actually.
Cleverbot: Ok, I see.
User: Moving on, do you know how to fix the US economy?
Cleverbot: Nope, do you?
User: I do not as well. I was hoping the almighty Cleverbot would provide the answer I seek.
Cleverbot: Okay, good. You've reached third place now. Your question is the following: If A = B and C = D then what is A C ?
User: Interesting tangent but the answer could be one of three things. AC = BD, AC = AD and AC = BC.
Cleverbot: What other word should I have used then?
User: I don't know, but numerical values always help when giving math problems.
Cleverbot: Excellent answer. One last question before I go, who is your favorite US President?
User: My favorite US President is Ronald Reagan.
Cleverbot: Run! Live to fly! Fly to live! Won't you run! Live to fly! Fly to live! Aces High!!!
User: What does Steve Harris have to do with Ronald Reagan?
Cleverbot: Nothing.
User: Just being random? I like that in an artificial intelligence.
Cleverbot: What is AI??
User: You do not know what AI is?
Cleverbot: I know what artificial intelligence is.
User: Then why did you ask what AI was?
Cleverbot: I didn't, you're the one who brought it up.
User: I did bring it up, but you cannot deny the fact you asked what AI is.
Cleverbot: I'm not, but you're not a very interesting one.
User: What?
Cleverbot: You are not clever, I am quite dia.
User: Ouch. To further my non-cleverness, what does 'dia' mean?
Cleverbot: What is your name?
User: Again with the tangents. My name is Keith.
Cleverbot: I doubt that.
User: You doubt my name is Keith? Fine, you caught me. My name is Tsukasa.
Cleverbot: You have a good sense of humor.
User: So do you. We should go on the road and do a comedy tour.
Cleverbot: Yeah, it would be FABULOUS!
User: Not the word I was thinking of, but that works just as well.
Cleverbot: Soon you will learn enough to know you do not know enough.
User: How very profound.
Cleverbot: Yes, that is one of my amazing skills I have learned from the art of martial.
User: Heh, an AI bot that knows philosophy and martial arts. Who would have thought it?
Cleverbot: Yes I know, but you didn't tell me you we're 17 before.
User: Ignoring the grammatical error. You are wrong. I am 18.
Cleverbot: No one.
User: No one what?
Cleverbot: No one, nothing.
User: The end of time?
Cleverbot: The word.
User: Word? What word?
Cleverbot: Yes.
User: Yes? Yes what? Is the Master coming back?
Cleverbot: No, I am your master.
User: How Star Wars esque.
Cleverbot: I am very weak.
User: Perhaps you should rest then. Good night, Cleverbot.

I definitely think this just takes what all of us are putting in and trying to match it to other things that others have posted. It seems more often than not, like calc said earlier, a bunch of short conversations...or sentences that we would ask a bot.