I'm really glad to see almost update to date list of SQL Server trace flags repository at SQL Server Central.
Though we use certain trace flags, we intend to forget the explanation about each trace flag so you can go-ahead and refer this anytime:
http://www.sqlservercentral.com/articles/trace+flags/70131/
Also take a look at the KB article http://support.microsoft.com/kb/920093 which talks about lot of unknown trace flags to improve performance on a heavy SQL Servers.
Here is a list of undocumented trace flags, DBCC commands, inline functions etc presented by Paul Randal in a SQL Server connections session
http://devconnections.com/updates/LasVegas_Fall10/SQL/Randal-SQL-SDB407-Undocumented.pdf
