I'm not a professional photographer so I don't have clients per se, but I've used both JAlbum and Lightroom's web gallery to create web galleries.
Mike.
P.S.
JAlbum is a bit clunky to work with at first, but it has good flexibility and many templates are available. Not related to photography, but you can see a gallery of some of my fractal images, created using JAlbum, here:
http://www3.telus.net/wolfnowl/Fractals/index.html (The 'Help' button explains navigation)