Y!Slow- Not so Slow
According to YDN's page:
YSlow measures web page performance based on the best practices evangelized by Yahoo!'s Exceptional Performance team. Since many of these best practices focus on the frontend, YSlow is integrated with Joe Hewitt's Firebug, the web development tool of choice for frontend developers.
Do give this tool a try along with FireBug. It woulr sure make a good combo.