A: Intel has a site, Intel AppUp, which is an easy-to-use store for Windows applications. You can search and browse the site, and it even has Angry Birds for the PC on it, which seems to be the in thing at the moment. Note that applications purchased from AppUp can be executed from outside the Intel AppUp application.
There are other sites, including Microsoft Product Scout, that help find products in a given category, such as ebook readers or media streaming. Product Scout has a special category just for slate PC applications.
If you're interested in Silverlight applications, go to this site, which has a great list of Silverlight applications that can be launched directly from your browser.