We have a couple forms that calls a cgi perl script action.
email is valid (at sign, period, 2 or 3 letter end, etc)
email is confirmed (either it calls up a popup that shows entered email and asks user if it is correct, or has the user enter it twice and compares)
required input items are entered (at least something, doesn't need to be validated)
After searching for preexisting scripts they do one of the above, but rarely all... or just too complicated to implement.