System objects - System objects such as sp_who2, sp_lock, fn_get_sql, etc. provide a simple means to capture basic metrics related to locking, blocking, executing code, etc.
Profiler - In a nutshell, Profiler provides the lowest common denominator of activity on a SQL Server instance. Profiler captures per session code with the ability to filter the data collection based on database, login, host name, application name, etc. in order to assess the IO, CPU usage, time needed, etc.
Perfmon\System Monitor - Perfmon\System Monitor is responsible for macro level metrics related to processes and sub systems.
Dynamic Management Views and Functions - New to SQL Server 2005 and beyond, the Dynamic Management Views and Functions offer a real time view into the SQL Server sub systems.
TYPEPERF.EXE - TYPEPERF.EXE is a command line tool included with the Windows operating system that writes performance data to the command window or to a file. It is necessary to capture performance data whenever you are trying to diagnose performance issues on a server. Performance data provides information on the server's utilization of the processor, memory, and disk, as well as SQL Server-specific performance data.
SQL Server Management Studio Built-in Performance Reports - As part of the installation of SQL Server 2005 and beyond a number of performance-related reports are installed. To get to these reports open the SQL Server Management Studio (SSMS) and connect to a SQL Server instance. If you don't have an instance of Reporting Services installed then the icon will be disabled.