How to find out what querry is a bottle neck, what is taking most time and resources?

Hello everyone!
I got an OLTP system (for www.realmofempires.com) which I am trying to analize.
It appear the SQL server takes the bulk of CPU usage, and althought it could be just load, I wonder if there are tools that I could use to see what (what querry perhaps) taking most time/resources.
I have a log of a running times, from client application perspective, of every single call to the database and I am unable to spot some long running querries this way but I optimized almost everything there and I am not sure how to move on.
It is possible that without some app redesign i cannot squeeze any more from the server but I doubt it. Likely I have some inneficiencies that I can spot simply by looking at the running time of some querries but I am really not sure how to move on, what to look for.
Can anyone suggest any tools, articles, books etc to help me shed some light on this?
Many thanks!!

Start a trace with the sql server profiler, set a filter for 5 seconds on duration. see what pops in. If 5 seconds is to short go to 10, 15 etc just to get the top set of queries taking a long time. Once the statements are identified you can look at them to determine any modifications. You can also use dmv's but thats a more complex topic.

You might want to take a look at Confio's Ignite product. I've used it some and it provides excellent WaitState analysis of bottlenecks and poorly performing queries.

Try performing a trace that captures these peaks in CPU usage and then use this free trace analyzer: www.dbsophic.com/traceanalyzer

In addition to those other great suggestions already mentioned there are a number of SQL Server DMV's that you can use to find statistics about the worst performing T-SQL statements and stored procedures. Here are a couple of articles I wrote on the subject that might help.
http://www.sql-server-performance.com/articles/per/Query_Execution_Statistics_p1.aspx
http://www.sql-server-performance.com/articles/per/Monitor_Stored_Procedure_Performance_p1.aspx
http://www.databasejournal.com/feat...erforming-T-SQL-Statements-on-an-Instance.htm