Client-side validation (checking for things like required fields, valid email address, etc) is always one of those sort of pain in the butt, last minute, only because i have to sort of things. It's not usually fun or flashy, it's just one of those things you have to do. Enter VanadiumJS, a new library just released by Daniel Kwiecinski.
Aside from having a cool-looking website, Vanadium looks like it will ease all of your validation woes, and make it easy and fun (you know, if you're in to that sort of thing) again. Worth checking out / bookmarking / using.