Eclipse's own Visual Editor:
<http://www.eclipse.org/vep/>

VE is nice.

I am running on Eclipse 3.1M6. WindowBuilder v4.0.0 supports this
Eclipse version.

You could look at WindowBuilder v4.0.0 http://www.windowbuilderpro.com/

This is a really nice product.

    * Support for Eclipse 3.1 M6 & Eclipse 3.0.2
    * Support for the SWT_AWT bridge allowing SWT and Swing to be mixed
          o New SWT_AWT palette
          o Embed any Swing widget into an SWT or RCP window
    * Support for JGoodies FormLayout
          o Graphically manage columns and rows
          o Graphically manage cell alignment and column/row spanning
          o Graphically reorder and resize columns and rows
          o Automatically handle gap columns and rows
          o Intelligently convert existing layouts to JGFL
          o Support for different units like pixels and dialog units
          o Support for all predefined FormLayout types
          o Support for grouping and ungrouping columns
          o Color highlighting for grouped columns and rows
          o Floating layout assistant for cells, columns and rows
          o Intelligently merge and split columns and rows
    * Support for new Eclipse 3.1 SWT elements
          o Support for the SWT Spinner & Link control
          o Support for the SWT TreeColumns
          o Support for virtual tables
    * Enhanced SWT support
          o Support for SWT DragSource & DropTarget and custom SWT
drag/drop transfer classes
          o Support for SWT TableItems & TreeItems
          o Support for SWT Cursor property
          o Support for strikeout and underline properties for SWT
fonts (Windows-only)
          o Support for new 3.0 SWT RowLayout properties
          o Enhanced SWT FormLayout support
    * Enhanced JFace support
          o Support for ApplicationWindow coolbars
          o Property support for JFace Action styles & accelerators
          o Icon support for SWT Dialogs, TitleAreaDialogs and
ApplicationWindows
          o Support for Shell events in ApplicationWindow
    * Enhanced Swing support
          o Support for custom Swing properties, editors and customizers
          o Support for instantiating custom JTable/JTree/JComboBox models
          o Added support for parsing and editing JTable columns
    * Enhanced NLS support
          o Enhanced NLS support to allow selection of any messages class
          o Added ability to auto-externalize strings for newly added
widgets
    * Editor & Property Pane enhancements
    * Code Parsing enhancements