John Resig's handy catch-all log (As seen in: "Secrets of the Javascript Ninja"). Amended with my own line number add-on for Chrome & Firefox. 2013.03.01 update: just added css support for chrome and console.time and console.timeEnd so you can track how fast your code is!

resiglogtrace.js

//John Resig's handy catch-all log (amended with my own linenumber add-on + new and improved CSS support for chrome!):
function trace() {//just cause I like "trace" better than his "log"
     try {
     var dA = navigator.userAgent.toLowerCase(), fF = dA.match(/(firefox)/);
     //show linenumber in FireFox & Chrome
	   if(fF){var lnVal = 1;}else{var lnVal = 2;}//fireFox sorts Error stack differently
       var linenumber = new Error().stack.split("\n")[lnVal], index = linenumber.indexOf("at "), clean = linenumber.slice(index+2, linenumber.length), cleaner = clean.split(":");
       console.log.apply(console, arguments);
       if(fF){
       		console.log("--------------------------------------------------------------- line:"+Array.prototype.slice.call(cleaner)[2]);
       }else{
       		console.log("%c ------------------------------------------------------------ line:"+Array.prototype.slice.call(cleaner)[2], 'color: #f60');
       }//if/else firefox
     }
     catch(e) { 
          try {opera.postError.apply(opera, arguments);
          }
          //careful! this will set off alerts in crummy browsers!
          catch(e) {
          	//alert(Array.prototype.join.call(arguments, "  "));
          }//second catch
     }//first catch
}//trace()

//console.time() and console.timeEnd() encapsulated to not throw errors in IE
function timeStart(){
	try {
       console.time.apply(console, arguments);
     }
     catch(e) { 
         //ie/opera
     }//first catch

}//timeStart

function timeEnd(){
	try {
       console.timeEnd.apply(console, arguments);
     }
     catch(e) { 
         //ie/opera
     }//first catch

}//timeEnd