ArcGIS REST API:

•  http://n2.nabble.com/Samples-using-new-ArcGIS-JavaScript-API-in-OpenLayers-td780603.html
•  http://dev.openlayers.org/sandbox/august/openlayers/openlayers-2.6/examples/ags/agsComprehensive-ext.html

 http://trac.openlayers.org/ticket/1749