With regard to a gift of money, Rav Shlomo Zalman says one must give maaser. There is no difference between earning money from business or from a gift. He adds that one should be sufficiently satisfied to receive 90% of a gift. If the gift is not money then you do not need to give any money to tzedoka based on its value but if and when you sell it you should then give 10% to tzedoka.
To another questioner however Rav Shlomo Zalman suggested that he value the gifts at the current price he can sell it at and give that sum to tzedoka when Hashem blesses him with sufficient means to pay it. (Aleihu Lo Yibol 1:YD:98)