Where have you been buddy ?? :) From IE-8 onwards, there is an in-built tool called IE Developer Toolbar packaged with IE. But you can still download and intall it anytime you want for IE-6 and 7. Its only 600kb or something.
Also, there is Firebug Lite , for any browser other than firefox. If you are too much used to Firebug, this will be good for you.
Hope this helps !!