Eclipse is a very popular IDE and many developers use it. If you'd like to use Eclipse to develop your Struts application, there are a couple of options:
The Completely Free Option
If you're a real cheapskate and don't want to spend anything at all on development tools, you will just need to install the Web Tools Platform (WTP) plugin. This Link contains a good article about WTP. To install WTP:
Make sure you have Eclipse version 3.2 or above loaded
Select help-->Software Updates-->Find and Install
Select "search for new features to install" and click Next
Select "Callisto Discovery Site" and click Finish
If you get prompts asking you to select mirror sites, just keep clicking OK
Expand "Callisto Discovery Site" and check the WTP option and click the Select Required button. This will add other prerequisite projects.
Click Finish and wait for it to install
Since Web Applications must run on a server, you will want to install a Java EE server on your computer before you begin developing applications. Just pick one and install it. Once you've installed the server, you can configure it to be used within Eclipse as a test server. The Eclipse help will tell you how to do this. Just select help-->help contents from the menu. Then expand "Web Application Development User Guide" --> "Using the Server tools" --> "Application Testing and Publishing" --> "Creating, Editing, and Deleting a Server" --> "Creating A Server". Follow the instructions for setting up a server and a server runtime environment.
Once you have installed WTP and configured a server, you're now ready to create a Struts Web project. Do the following:
Select file-->import from the menu
Expand the web folder, select WAR file, and click next
Click the Browse button next to the WAR file text box. Navigate to the directory to which you unzipped the struts download file and select struts-blank-1.3.5.war (or similar), which is in the apps directory.
Back on the WAR Import panel, enter a name for your project in the Web Project field, select a target runtime, and click finish
The above process will give you an Eclipse project that has all the basic Struts artifacts already set up for you. All you have to do now is start coding Action classes, JSPs, etc.
The WTP tools are general web development tools, and are not specific to Struts, but they will be a great help in developing your Struts application. The WTP does provide ctrl+space auto-completion for JSPs (Including Struts custom tags) and for the struts-config.xml file.
News Flash! Exadel Studio Pro, which is currently a commercial Eclipse Plugin for Web Application Development is expected to become an open source project in the summer of 2007. It will be released under the name "Red Hat Developer Studio". Here's the link
The Almost Free Option
If you've got about $50 (USD) a year to spend on development tools, you'd do well to check out MyEclipse. It has some good web development tools as well as tools that are specific to Struts.