http://gis.stackexchange.com/questions/2393/will-postgresql-9-work-with-arcgis-10

For Editing Postgis
ZigGIS 3.0

http://groups.google.com/group/ziggis/browse_thread/thread/8e17f4c2ac57f428?hl=en


Read Only can be done via the right [ODBC Postgres Drivers][1] and doing a direct connection in ArcCatalog


  [1]: http://psqlodbc.projects.postgresql.org/