There are free web sites that let you create a web-based chat room on the fly. Then you just send people the URL of your chat room and they can chat with you.
Here are a few sites we like:
TodaysMeet - nice simple interface (you can ignore the twitter hashtag field- just name the room and go.)
TinyChat - a few added options, such as embedding. Note that you do not need to sign in with MySpace, Twiiter, or Facebook, you can just type your name in the box and go.