DMVs with information on connections, sessions and requests

select * from sys.dm_exec_connections

Returns information about the connections established to this instance of SQL Server and the details of each connection.

http://msdn.microsoft.com/en-us/library/ms181509.aspx

select * from sys.dm_exec_sessions

Returns information about the authenticated sessions on SQL Server.

http://msdn.microsoft.com/en-us/library/ms176013.aspx

select * from sys.dm_exec_requests

Returns information about each request that is executing within SQL Server.

http://msdn.microsoft.com/en-us/library/ms177648.aspx