entry for purchase goods free of cost

you have to pass entry for the amount paid towards custom duty and frieght  

For taking goods into stock u can pass the purchase entry for NIL amount.

As u are receiving sample material as free of cost the value is nil. but customs paid on goods and if no credit will available for this u may Debit the

purchase A/c Dr. (Custom duty)

To, Bank A/c (Custom duty).

For freight charges, freight inwards A/c Dr.

                                    Service tax of freight A/c Dr.(in case specified person)

                                   TO Transorter/cash/Bank

                                     to Service Tax payable

What if the samples are used in production i.e. purchase not booked but material consumed.