1) Download Microsoft SQL Server Report Builder 3.0 for Microsoft SQL Server 2008 R2: This is top highlight as it brings the Map control and Bing Maps capabilities, Sparklines, Databars, and Report Parts Gallery.
2) Download Microsoft SQL Server PowerPivot for Microsoft Excel: Business users would not want to wait and download it ASAP and try out the potential of Powerpivot.
3) Download Microsoft SQL Server 2008 R2 Books On-line: My personal favourite. It's always advantageous to stay up-to-date with the latest reference material.
4) Download Microsoft SQL Server 2008 R2 Best Practices Analyzer: This latest best practice analyzer is available now. So stop playing with the old 2000 / 2005 version analyzer and get this shiny new analyzer for your shiny new R2 version of SQL Server.
5) This is not a part of the Feature pack, but I thought of mentioning it as it's a very valuable resource. It's a introductory level " Free SQL Server 2008 R2 Ebook ".
Above list is not the exhaustive list. Entire feature pack can be downloaded from here.