While we're on the topic of lightweight JS validation libraries, I released my own and have used it for well over a year on a number of production sites. It's quite feature rich and also very low on LOC. It already includes much of the support you guys mentioned here, including live validation and support for passing params. It's garnered towards those already utilizing jQuery sitewide who like things short and sweet. You can override and customize everything, but it also provides you with decent defaults.
The version I use now is tweaked with improvements. I'll gladly share it; I've just been busy and not posting much to the site. If you see problems with the validation methods, they've been fixed over the year in the new version.
Salid - The Simple jQuery Form Validator
http://www.jqueryin.com/projects/salid-the-simple-jquery-for...
The version I use now is tweaked with improvements. I'll gladly share it; I've just been busy and not posting much to the site. If you see problems with the validation methods, they've been fixed over the year in the new version.