Unwanted characters in a URL

[dartho]

Someone asked me to write a plugin which adds the threads title to URLs - for example if teh thread is call "What is your name & age?" they'd want URL's to be written as .../showthread.php?t=737&thread_title=What-is-your-name-and-age

this is pretty simple to do, but I was wondering what sort of things would need to be removed from the title to make sure the created URL is valid

I've a few such as '&' (vbulletin nicely removes the ampersand and puts this in),'?' and accented characters - what other things do we not want appearing in URL's ?

Thanks