I know of YSlow with Firefox and http://webwait.com/ .
Any other services around?
As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance. If this question can be reworded to fit the rules in the help center, please edit the question.
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
Google-Chrome and Opera have builtin tools to analyze websites, including loadtime.