For those of you that have been wanting to try out SQL Server 2008 R2, you can download the November CTP of Express here (posted yesterday) and the full version of the November CTP here. This is version 10.50.1352.12. The full version is an evaluation edition and will expire after 180 days. I am not sure when the full version of the CTP was posted publicly; earlier this week, that privilege was restricted to MSDN / TechNet Plus subscribers (and TAP a.k.a. early adopter customers).
For the Express Edition, if you scroll down the page, you will see that you can also download the Express version of Management Studio (SSMSE) for both 32-bit and 64-bit systems, without having to download the entire engine and other services. This was announced earlier today by @SQLAzure in a blog post. In previous releases of Express, it wasn't always easy to find the Management Studio Express Edition downloads, and they often came later than the combined downloads (w/Tools or w/Advanced Services). Most users ended up downloading one of those and then trying to install just the management tools.
For those of you who are unwilling to download any of these pre-release builds onto your machines, and who don't have virtual machines you can use for this purpose, you can get limited exposure to the new engine and some of its features by signing up at sqlserverbeta.com (you can read more about this program in a recent blog post by Jorge Segarra (@SQLChicken)). Currently their front page advertises a lab for the August CTP (build 10.50.1092.20), but this could just be a lag in marketing materials. So I'm not sure if they are currently offering the latest CTP build of R2, or if you will have to wait for that to become part of their offering.