I know of YSlow with Firefox and http://webwait.com/ .
Any other services around?
Web Applications Stack Exchange is a question and answer site for power users of web applications. It only takes a minute to sign up.Sign up to join this community
In addition to YSlow and WebPageTest mentioned in other answers I use the LORI (life of request information) extension for Firefox during development to give a quick indication of page speed.
It adds a few fields to the status bar to give you a quick overview of some important figures: time to first byte, time to completion, total size, number of requests