this book has some excellent information about the Optimizer
http://www.amazon.com/Microsoft-SQL-Server-2008-Internals/dp/0735626243/ref=pd_sim_b_2"> http://www.amazon.com/Microsoft-SQL-Server-2008-Internals/dp/0735626243/ref=pd_sim_b_2
infact the entire
Inside Microsoft SQL Server series is excellent in helping understand the internals of SQL server.