I am not sure if the below ebooks from red-gate were free for a while, but I just discovered it and thought that you guys might be interested in that as well.
Here is a snipp from:
Ebook versions of the Best of SQL Server Central Vol 1 and the Best of SQL Server Central Vol 2 are available for download. These ebooks are full of "essays and ideas from the SQL Server community," and are a valuable resource for anyone working with SQL Server.