While trying to use appropriate icons with buttons and fields, If you are looking for how to find out all available icons, pictograms and graphics for use in your WebDynpro Application.
Check out the test application WDR_TEST_WEB_ICONS to see various available graphics / icons and there path ( ~Icon/* ) to be used in your code.
Simply run the webdynpro application under the Webdynpro component WDR_TEST_WEB_ICONS to see the list of all the icons, web icons & workset images and pictograms or Or just navigate to the URL 
: http://<hostname:Port>/sap/bc/webdynpro/sap/wdr_test_web_icons?sap-language=EN
This will execute a ready-to-run demo applications on how to use graphics element in your WebDynpro development.
List of Work centers graphics.
This demo application is contained within package SWDP_DEMO which is delivered in your system. 
It contains many other sample codes for demo or testing on different topics you may encounter while developing Web Dynpro for ABAP components and applications.