OpenSim Resources

OpenSimulator
Official OpenSim development site. Wiki resources include opensim stand-alone/grid set-up guides, extensive information about OpenSim itself, source code and 3rd party binary distros, as well as support portals (Detailed below)

realXtend
Private organization adding advanced functionality to the open-souce SL viewer and OpenSim

Idiot's Guide to OpenSim

Communication Channels:
IRC Channels: #opensim and #opensim-dev on Freenode
Mailing lists: Opensim-users, Opensim-dev, Opensim-commits (SVN)

Grids:
OpenLifeGrid
Resources: Chat rooms, forums, comprehensive user portal, stand-alone opensim binaries, wikis/guides

OSGrid
Resources: Forums, user portal

DeepGrid
Resources: User portal

Full List of Grids