Cleaning user data

I'd like to canvas opinions about what's needed to clean user input. I'm using an HTML form where users enter simple things like name and phone number, but also a couple of small text areas for address and a message (up to 50 words or so). How would people recommend cleaning this data when it's received (via $_POST) in the next page? Some fields (like email) I can check against a template using ereg(), but the text areas pose more of a problem. I assume running strip_tags() might be a wise precaution, and maybe also htmlentities(). Anything else? I'd be interested to hear what other people do. a+ Steve