Stockpile Cards

Stockpile Cards
Stockpile Cards is a term I use to describe the group of cards that you should save for the last turn. There is no definitive list of Stockpile Cards since the value of each card partly depends on the other cards in play. The list below is intended to point out the types of cards you should save and why. The cards below are particularly worth saving for the last turn:

Eden: Whenever you play Eden (a P4 planet) it immediately becomes a target. If you play Eden early in the game, odds are that you won't have it at the end of the game. If you get Eden, you often will want to discover it during the last turn.
Barchan, Freya, Taurus: If you can't get Eden, try to save one of these P3 planets.
Dictatorship, Domed Cities, Megalopolis, Space Station PT1, Space Station PT2, Terraform: Each of these Civilization cards adds 1 to the Population Potential of a planet. These cards are extremely valuable on the last turn because you can build as many as you want wherever you want (in your own Empire). During the Build phase of the last turn you will want to build these cards as evenly as possible so that no one planet is too valuable. The exception would be if you are sure you can defend one planet, you might want to build them all on that planet.
Fast Scout Ship: This card allows you to steal another players newly discovered planet, effectively letting you discover two planets in one turn. Saving this card until the final turn allows you to grow rapidly while only being a target for the last turn. Note that other players may also be playing Fast Scout Ship on your planet, so you may need a Fast Scout Ship just to stay even.
Koolian Explorers: The card allows you to discover a second planet during your turn, giving you Population Potential a last turn boost.
Peace Treaty, Quantum Flux, War and Peace, Warp Cannon, Wormhole, Suicide Attack: All these cards allow you to deflect attacks on your planets. You want to keep these cards until the last turn, if possible, so that you can withstand several attacks during the last turn.
Military Academy, Antarian Auditors, Terran Shock Troops, Koolian Commandos: These cards all allow you to unexpectedly increase your strength in the middle of an attack. Thus, an attack may look successful until you elect to activate one of these cards---like having cavalry come over the hill at just the right time. At the end of the game most players will forget that you have these cards and will not account for them when they attack you.
Temporal Rift: This card is particularly valuable during the last turn. You can use it to either discover a second planet or attack a second planets. Timed correctly, this could give you a last minute boost in your Population Potential that is hard for your opponents to match.