Let's face it, writing any application these days, be it for a rich client or a thin one, starts off as if you're in a restaurant choosing from a menu. You're presented with a set of choices for this framework or that framework, some of which are de facto choices, others that may be less appealing. There are side dishes of controls you might want to use, so you have to select them as well.
Because you're here reading this post on this particular website from this particular .NET control and framework vendor, we're going to assume that your number one, automatic choice will be the .NET Framework. A given, you might say. Ditto for our controls, because obviously you have good taste.
But what about other frameworks? Obviously we have ours for creating an ORM (eXpress Persistent Objects) or for creating an MVC type application (eXpressApp Framework), but there are some others out there, open source, that you might want to investigate to polish the user interface of your apps. Here's a brief selection and please note I don't pretend to be thorough here.
Let's start at the top, in your users' face, as it were. Cascading Stylesheets (CSS) have been the way to style to look and feel of your web apps for a long time. But did you realize that there were frameworks for CSS?
Yahoo!, as part of their various developer products, have a CSS framework called YUI Grids CSS. No, not grids in the way we use the term, but grids that help you layout your web pages. There's a builder application that helps you explore the layouts you can create with the YUI Grids CSS, and you can get the HTML code once you've worked out a layout you like.
A better one, in my view, is Blueprint CSS. Again it's a grid based framework that gives you the ability to go to 24 columns across. Before you go, what the..., let me explain that in general you merge columns newspaper style, you don't try and put 24 columns on the screen at the same time. The grids, if you like, allow you to layout your content as if you were in a graphics app ("snap to grid"). Blueprint also comes with some good looking (and consistent) font choices for your various HTML elements.
If you prefer something a little more accepted and widespread, there's always Prototype. It has good class inheritance functionality through its Class module. Prototype has some excellent AJAX functionality as well, although you'd presumably be using ASP.NET AJAX. I don't know too much about its DOM manipulation features, because I much prefer the next framework in my list.
Presentation layer frameworks
This is kind of a mind bender in a way. The application is not displaying a web page from out there in internet-land, it is just using HTML, etc, as the presentation layer for a normal desktop application. In other words, this isn't Google Chrome's "Create Application Shortcut", which is just a way of using Chrome without the chrome for a particular web site.
Adobe Air is downloadable for free, but in case you want an open source, no mega-corporation framework instead, try out Titanium.
Of course, in the .NET world, there's WPF and Silverlight. Both of which we support with an ever-growing set of controls.
So, go on, have some fun investigating frameworks for your next application and save some time by using them.