Here is a short list of resources for SQL Server performance tuning:
A good place to start is the excellent web site: http://www.sql-server-performance.com/
It covers basics and more advanced issues both from the DBA and developer points of view. Very readable.
SQL Team often has articles relating to performance.
Greg Linwood’s blog is a mine of information on performance tuning: for instance this article on Query Plan Guides (SQL Server 2005 only). Greg gave a great introduction to performance tuning a few months ago in Perth: the slide deck is here.
The SQL Server Query Optimisation Team also has an excellent blog, with articles like this one on Automated Auto-Indexing.
Ken Henderson’s SQL blog is here. Bart Duncan started blogging just recently, he is a recognised master. His weblog is here
Also check out webcasts by Kimberley Tripp, Bob Beauchemin and Bill Graziano to name a few. The main webcast events page is here. There is a whole section devoted to SQL Server here. There are more to watch than I can find time! These are a remarkable free resource.
There are some great books available:
SQL Server Performance Tuning Distilled by Sajal Dam is a good nuts and bolts introduction with examples.
SQL Tuning by Dan Tow is excellent but takes a bit of work to get your head around. Applicable to Oracle and many other databases.
The Guru’s Guide to SQL Server Architecture and Internals by Ken Henderson. Very thorough treatment of what’s under the hood. Not directly related to solving a particular performance problem but if you want to understand how the internals affect the layers above this book covers it in great detail.