The Gemara (Berachot 58b) and the Shulhan Aruch (Orah Haim, 225:8) say that one who sees all sorts of peculiar types of human beings, such as one who is lack, red, or white, or who is very small should recite “Baruch Ata…Meshane Haberiot” (“Bless are Thou…Who changes the creations”). On the surface it seems offensive to make a blessing based on one’s race, but Rashi comments that the Gemara does not refer to one that would be known today as “Black” (African ancestry) or “White” (European ancestry). Rather the Gemara refers to one who is abnormally dark or light and the like. As a matter of fact, Rabbi Ya’akov Hagiz (Hilchot Ketanot) says that the Gemara refers to someone black who was born to white parents, or vice versa.
The Shulhan Aruch continues by saying that this blessing is also recited when one sees an elephant or a monkey. Thus one would be able to recite this blessing at a zoo if one see the aforementioned animals.
Furthermore, the Shulhan Aruch (ibid:10) says that if one sees beautiful trees, or beautiful people, even non-Jews, one recites “Baruch Ata…Shekacha Lo BeOlamo” (Blessed art Thou…Whose universe is such”). Since normally it is forbidden for a man to gaze an unknown woman, and much less recite a blessing, it is explained that what’s involved is not staring, but rather a quick glance. Nevertheless, it does not appear that the recital of this blessing is common nowadays. Rabbi Avraham Danzig (Haye Adam) explains that this blessing can only be recited once in one’s lifetime. Since one likely saw beautiful trees or people previously and did not recite a blessing, one missed the opportunity. The Sha’ar Hatziun (O.H. 225:33) says that people nowadays lack the capacity to judge who or what is truly beautiful and deserving of a blessing. However, one is permitted to recite the blessing without Hashem’s Name.
Regarding today’s (August 21, 2017/29 Av, 5777) solar eclipse, Rabbi Haim Kanievsky was asked whether a blessing is recited just as it is for other rare phenomena like comets and rainbows. He quotes the the Gemara (Sukkah 29a) which says that when the sun is “struck”, that is, is eclipsed by the moon, it is a bad omen for the world, and as such,a blessing should not be recited.
Summary: If one sees very beautiful animals, trees or people, one can recite“Baruch Shekacha Lo BeOlamo”, omitting Hashem’s Name. A blessing is not recited of a solar eclipse.