Redeeming secondary tithe which is in a different location, on "the coin I will remove from my purse," so that the redemption will actually be retroactive: Eruvin 37b
Extending the boundary of Shabbat travel if the extension was established with a Bi-directional option: Yoma 56b; Eruvin 36b-38a
Setting up the meal which extends the limit for travel on Shabbat [Techum], and deciding afterward who will be the participants in the meal and for what time frame it will be used: Eruvin 37b
Deciding after Shabbat begins to use a meal extending the limit one may travel on Shabbat, if it was set up one's behalf before Shabbat began: Eruvin 82a
Considering an item purchased by partners to have parts of it owned by each individual partner, so that it will be as though they had each donated a part. The practical application would be to use this jointly-owned item for a symbol of the merger of adjacent properties, to permit transportation between them on Shabbat: Eruvin 71b
Designating a set of birds as those from which one will select his meal on Yom Tov, and then retroactively identifying the specific one on Yom Tov: Beitzah 10a-b
Retroactively nullifying impurity from affecting the entrances to a house that contains a corpse, by identifying which entrance will be used to remove the corpse: Eruvin 68a; Beitzah 10a
Retroactive identification of the woman for whom a Get was written: Zevachim 3a