Query Twitch.tv to see if a channel is streaming! Assumes a div of id = 'streaming' to put the results, and a couple css classes to style the results.

Twitch.tv is channel live api query

<script type="text/javascript"> 
$(document).ready(function() {
    
    // your twitch channel name
    var twitchName = 'yourchannelname'
    
    // an element on your page to put the widget into
    var elementSelector = '#streaming'
 
    // HTML to display while waiting for data
    var loadingHTML = "<b class='twitchLoading'>Querying twitch.tv...</b> <a href='http://www.twitch.tv/" + twitchName + "'>http://www.twitch.tv/" + twitchName + "</a>"
    
    // HTML to display while online
    var onlineHTML = "<b class='twitchOnline'>*ONLINE*</b> <a href='http://www.twitch.tv/" + twitchName + "'>http://www.twitch.tv/" + twitchName + "</a>"
 
    // HTML to display while offline
    var offlineHTML = "<b class='twitchOffline'>*OFFLINE*</b> <a href='http://www.twitch.tv/" + twitchName + "'>http://www.twitch.tv/" + twitchName + "</a>"
    
    $(elementSelector).html(loadingHTML)
 
    $.getJSON(
        'http://api.justin.tv/api/stream/list.json?channel=' + twitchName + '&jsonp=?',
 
        function (twitchData) {
            if (twitchData && twitchData[0]) {
                if (twitchData[0].stream_type && twitchData[0].stream_type === 'live') {
                    // live
                    $(elementSelector).html(onlineHTML)
                } else {
                    // something other than live
                    $(elementSelector).html(offlineHTML)
                }
            } else {
                // no data or invalid data from twitch
                $(elementSelector).html(offlineHTML)
            }
        }
    )
})
</script>