With SQL Server 2005 Microsoft introduced a new set of so called Dynamic Management Views (DMV).

The following views could be a good starter when searching for specific information in or around your SQL Server:

SQL Server related DMV

sys.dm_os_sys_info
sys.dm_os_hosts
sys.dm_os_schedulers
sys.dm_io_pending_io_requests
sys.dm_io_virtual_file_stats
sys.dm_os_memory_clerks
sys.dm_os_ring_buffers

Database Related DMV

sys.dm_db_file_space_usage
sys.dm_db_session_space_usage
sys.dm_db_partition_stats
sys.dm_os_performance_counters

INDEX Related DMV

sys.dm_db_index_usage_stats

Execution Related DMV

sys.dm_exec_sessions
sys.dm_exec_connections
sys.dm_exec_requests
sys.dm_exec_sql_text