Performance Monitor (perfmon) and dynamic management viewws (DMV's) are best. You can also browse the trace events from a server side trace on the client machine using Profiler. I would not recommend running Profiler against a production system directly. You can also look at the Activity Monitor through Management Studio, but that's just showing you the output of queries against the DMV's.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning