Halachos for Erev Shabbos Kodesh
1) Ma'aser money may be used to support "Kiruv" organizations whose mission it is to help our non religious brothers and sisters find their way back to our father in heaven. (Bais Dino Shel Shlomo. Dayan Yisroel Yaakov Fisher Zatzal even allowed using Ma'aser money to pay for "Kiruv" courses.)
Ma'aser money should not be given to charity organizations run by non religious Jews. (Psak of Rav Shmuel Auerbach Shlita)
2) A yeshiva or school that you or your children attended doesn't have halachic precedence for your Ma'aser dollars over a different school or Tzedaka. However, due to the Hakoras Hatov (appreciation) due the school, you should indeed financially support them over a different school. (Psak of Rav Asher Weiss Shlita)
Halachos for Shabbos Kodesh
There are too many references in Chazal and the Poskim regarding the importance of giving Ma'aser to quote them all.
But, to end our study of this topic on a powerful note, I will quote a small sampling of their holy words regarding the "power" of Ma'aser:
Properly separating and giving Ma'aser causes a person to become wealthy (Talmud Shabbos 119b. See also Rabbeinu Yonah's commentary to Pirkei Avos Perek 3 Mishna 13)
Although it is prohibited to "test" Hashem, there is an exception when it comes to Ma'aser, as the Posuk (Malachi 3:10) states "V'Chanuni Na B'Zos amar Hashem- Test me with this, said Hashem" (see Malbim's explanation this Posuk. See also Me'iri to Taanis 9a. See Shulchan Aruch Y"D Siman 247:4 that this exception is only for Ma'aser and not all Tzedaka. Rabbeinu Bachya in the introduction to Parshas Ki Savo disagrees, and maintains that one may test Hashem with all Tzedaka)
In the merit of properly giving Ma'aser, a person's prayers will be answered (Mateh Moshe Vol. 2 Ma'alas Tzedaka Chapter 8 based on the Midrash)
Properly giving Ma'aser can help save a person from sicknesses (The Steipler Zatzal based on Midrash Bamidbar Parsha 9 Siman 671)
Properly separating Ma'aser can prevent miscarriages (Chazon Ish, story quoted in Sefer Maaseh Ish Vol. 1 Page 144. This is also the advice of Rav Chaim Pinchas Scheinberg Shlita to people who have a tendency to miscarry, and it has worked on countless occasions.)
TAM V'NISHLAM HILCHOS MA'ASER KESAFIM. YISHTABACH SHEMO SHEL HAKADOSH BARUCH HU!