A more scalable solution that doesn't require serialization is this:

    CREATE PROCEDURE [dbo].[uspGetNextID]
    (
      @inID BIGINT OUT
    )
    AS
          SET NOCOUNT ON
          INSERT INTO SequenceTable DEFAULT VALUES -- Empty table with an IDENTITY column;
          DELETE FROM SequenceTable WITH (READPAST);
          SET @inID = SCOPE_IDENTITY();
    RETURN;