Microsoft has released Windows 7 and Server 2008 R2 Service Pack 1 RC to public which can be downloaded using following Direct Download link
SP1 will not contain any new features that are specific to Windows 7 itself. For Windows 7, SP1 will simply be the combination of updates already available through Windows Update and additional hotfixes based on feedback by customers and partners.
This RC version will insert a time-bomb in your Windows. It’ll add an expiry date of Nov 30, 2011 to your Windows. So you can use your system till Nov 30, 2011. After that you’ll need to either upgrade to final version of SP1 or uninstall RC version of SP1 to be able to use your Windows.
It also add a watermark on your Desktop which says:
Evaluation copy. Build 7601