Service Pack 1 Release Candidate for both Windows 7 and Windows Server 2008 R2 now available
While Service Pack 1 is mainly a collection of all the previous updates the OS has received, there are a couple of interesting additions, namely RemoteFX and Dynamic Memory. RemoteFX enables host-based rendering of 3D graphics, allowing you to get the same rich graphic abilities you have on your machine even when you're remotely connecting to another computer. Dynamic Memory allows servers using Hyper-V to use memory more efficiently.
The final version of SP1 for both Windows 7 and Windows Server 2008 R2 is expected to hit in the first quarter of next year. And unless you need to test the state the SP is in now, you'd probably best wait for that to ship.
In case you want to download the RC, you need to go here and follow the instructions.