basic validation wuestion for username/emails...

hi.. rather than recreate the wheel.. i'm looking for samples of good/solid/comprehensive validation functions for user/form inputs. specifically, i'm looking for ways to validate/verify that the user has entered valid username/email. as i go forth, i'll be looking for address/zip/phone/etc... as well. doe you guys have any solid functions that you've created, or any particular libraries that you use (open source) that handle form input validation issues?? i've seen various sites/srticles on google, but i figured i'd ask here as well. thanks bruce bedouglas@earthlink.net