Here is a nice little start-to-finish tutorial from Nettuts for creating a register form for your WordPress site, covering the markup, the CSS, jQuery and the WordPress code. We are starting to run across paid-for solutions for registration forms that are almost as easy to insert into your site’s code as a blog post, but which result really attractive, professional looking forms.
At the same time it behooves even non-professionals to have some inkling as to how to create their own forms for their sites, because it’s important to have a customized sign-up to fit the overall aesthetic of your site. It should also be clear that it you are a developer you could use this tutorial to learn how to create registration forms for clients!

