According to a few sources (e.g. Gail Shaw and Brian Randell), Microsoft announced today at TechEd South Africa that SQL Server 2008 has RTM'd. For those that aren't aware, this just means that the code has been signed off, not that it is being placed on store shelves today. It takes some time to manufacture and distribute media, so I am not sure when it will be available at the retail level. But the download ISOs are available from MSDN Subscriber Downloads and TechNet Subscriber Downloads right now! You will notice that the following editions are available: Developer, Standard, Enterprise, Web and Workgroup. I'll be watching for the availability of Express Edition, which is absent from the list at this time. Also note that if you are using IA64, the only editions available to you are Enterprise and Developer. Not sure if that is temporary or permanent, or for how many of you that might actually be relevant...
And if you aren't one of the lucky ones with an MSDN or TechNet subscription, 180-day trial software (Enterprise Evaluation Edition) is available here. You will also find links to demos and virtual labs, where you can get a taste for the new version without having to download or install anything.
For those interested in the build #, @@VERSION returns:
Microsoft SQL Server 2008 (RTM) - 10.0.1600.22 (Intel X86)
Jul 9 2008 14:43:34