This software is pretty basic, but powerful.
It can broadcast the audio from your computer, and also has another channel for an audio input like a microphone.
It also comes with a basic mixer to balance these sounds in the main mix.
Would recommend!
Wohooo.net - Create Your Own Online Radio Station
SHOUTcast Radio - SHOUTcast Radio is the home of free Internet Radio.
Streampusher - Start your own internet radio station
Live365 - 5,000+ online radio stations run by real people, not generated by computers.
Radio Mast - Embed live streaming audio on your website. Streaming audio platform with radio stream hosting and stream monitoring for broadcasters, radio engineers, and agencies.
Listen2MyRadio - Stop dreaming, start streaming. Free and premium Shoutcast and Icecast audio broadcasting.