This is an updated version of a similar blog we've written a while back. There are a few different Solaris distributions out there produced both by Sun and the Open source community. Here is a quick run down on the differences. The OS source code is distributed at http://opensolaris.org.
Bleeding Edge - Community/Developer
OpenSolaris 2009.06 (Indiana releases)
* Based on OpenSolaris
* This comes with a live CD
* It is released in a 6 month cycle (or twice a month for Development builds)
* Updates are not available
* Uses IPS packaging: http://pkg.opensolaris.org/dev
* Free
Sun Supported
OpenSolaris 2009.06 (Indiana release, with updates)
* Updates available for 6-18 months through https://pkg.sun.com/opensolaris/support
* Can file bugs and get phone or forum support
* Subscription fee
Solaris 10 5/09 update 7
* Six month updates
* SPARC and x86 platforms
* SRv4 packaging/repo
* Free to download and use
There are also several other Open Solaris distributions. One of which is NexentaOS, a OpenSolaris based OS topped with GNU software.
Update Aug 26th 2009: Removed SXCE, Sun is going to EOL SXCE and go in favor of the Indian Releases for future supported versions of OpenSolaris. That makes much more sense now, never understood why it wanted to have two different forks.