My vote's on jQuery, but whatever you do, do it unobtrusively (one reference: http://simonwillison.net/static/2008/xtech/ http://simonwillison.net/static/2008/x

My vote's on jQuery, but whatever you do, do it unobtrusively (one reference: http://simonwillison.net/static/2008/xtech/ http://simonwillison.net/static/2008/xtech/ ). It's easy if you do it from the start, and there's a real savings in maintenance costs.