Connecting the requirement for the Mitzvah of special philanthropy, with that of reading the Purim Story: Megillah 6b
Sending two gifts to two people, as the minimum obligation: Megillah 7a
When the requirement falls out, if Purim is on Shabbat: Megillah 4b, 5a
When the requirement falls out, if there are two months of Adar: Megillah 6b-7a
Uses
Minimizing communal expenditures for Matanot la'Evyonim, or splurging: Bava Metzia 78b
What happens to leftover matanot la'evyonim: Bava Metzia 78b