Removing all characters that are not #'s or letters

[blackdog]

Is there a function that will remove all characters that aren't letters and numbers? I'm doing a mod_rewrite to include the title of the page in the URL and i don't want punctuation, etc to show up in the url

thanks!

[logic_earth]

$r = preg_replace('/[^a-z0-9]+/i', '', $s); 

[blackdog]

thanks! but how can i modify that to keep spaces or dashes?

[logic_earth]

$r = preg_replace('/[^a-z0-9 \-]+/i', '', $s); 

[blackdog]

thanks!