Once deciding on this, another vexing conundrum presents itself. Unlike Flash and Sliverlight, which Esri has web mapping API's for as well, there is not just a single integrated development environment (IDE) with code assist built in. Adobe distributes the Flash Builder IDE and it has some great code assist built in. Microsoft's Visual Studio provides outstanding code assist for developing Silverlight.
One thing not directly discussed in this document is the only code editor with code assist available is Aptana Studio 2. This is important to note since the current release is Aptana Studio 3. As a result, you have to make sure to download and install Aptana Studio 2 if you want to be able to have code assist available.
Successfully installing this jar file requires unzipping the zipped archive, copying the jar file into the Aptana plugins folder and enabling it in Aptana. If like myself and installing Aptana for only the current user, the plugin folder can be difficult to locate. Instead of being located in the C:/Programs directory where all other programs installed on a Windows computer are, Aptana is installed in C:/Users/<loginName>/AppData/Local/Aptana Studio 2.0. Inside this folder is located inside the Aptana folder at C:/Users/<loginName>/AppData/Local/Aptana Studio 2.0/plugins. Copy the jar file from the zipped archive downloaded from Esri into this directory.
With the jar file copied into the plugins directory, enable the plugin from within Aptana Studio. Go to Window > Show View > References to open the References dialog. In the References Dialog, open the Global References and check the box next to ArcGIS JSAPI.