The Struts custom tags aren't the only tag libraries that work with Struts applications. Although some of the Struts tags make it very easy to use certain facets of the framework, other tags can assist you in developing applications and help to reduce the development time for a project.
We will mention only two of the more popular locations at which you can find additional tag libraries, but many other sites and vendors provide free or low-cost tag libraries too. You should always check to see if the tag you need already exists or if there's one that's close enough for you to simply extend or modify.
One of the best resources is another Jakarta project named Taglibs. The goal of the Taglibs project is to provide an open source repository for JSP custom tag libraries and web publishing tool extensions.
There are around 25 separate tag libraries in the Taglibs project, each of which provides some unique functionality that most web applications need to perform sooner or later. The tag libraries are free and provide the source code, which allows you to not only get a better understanding of how to develop JSP tags but also to modify or extend the tags as your application dictates.
There's no sense in listing the available tags, as new ones are added regularly. The best idea is to check the site itself. You can find the Taglibs project on the Jakarta site at http://jakarta.apache.org/taglibs/.
Another useful web site that contains many JSP tags is http://jsptags.com. This site has been around for several years and has many tag libraries that you can use for free. It's also a great resource for other web application information. Make sure to check this site as well before setting off to create your own tag. Somebody may have already created the tag you need, saving you the development and testing time—always a good thing.