SQL Server - How to get the name of the logged in user?

[Clearcode]

How do I get the name of the user executing a stored proc in the T-SQL in that proc?
e.g.

ALTER PROCEDURE dbo.TakeOnClient
   (
   @Id uniqueidentifier
   )

AS
  DECLARE @Username varchar(200)

  -- Get the current login that executes this proc

  -- Update the client table
  UPDATE dbo.Clients
      SET Owner = @Username
   WHERE Id = @Id

RETURN

[Shuja Ali]

how about using this??

SELECT 'The current user is: '+ convert(char(30), SYSTEM_USER)

[Krzemo]

Or use:

SET Owner = SUSER_SNAME()