One of the most popular programs in computer science is the Eliza program. This program simulates that you are talking to a person when in fact you are having a conversation with a computer program. Here is a link to a Web-based version of that program.
Wikipedia (http://en.wikipedia.org/wiki/ELIZA) provides a nice history behind this program. Here is an excerpt:
“ELIZA is a computer program by Joseph Weizenbaum, designed in 1966, which parodied a Rogerian therapist, largely by rephrasing many of the patient's statements as questions and posing them to the patient. Thus, for example, the response to "My head hurts" might be "Why do you say your head hurts?" The response to "My mother hates me" might be "Who else in your family hates you?" ELIZA was named after Eliza Doolittle, a working-class character in George Bernard Shaw's play Pygmalion, who is taught to speak with an upper class accent.”
I think it would be great to add an avatar interface to this program. Try out the Web-based version previously mentioned and then imagine how the program would work with an avatar.