In the games
Lucky Star, Touhou Project and other shooters
The value varies depending on how high the player is up on the screen. Several other factors can also affect their value, depending on the game. Each one is worth 100 - 2,000 points if playing on Lunatic, 100 - 1,500 if playing on Difficult, or 100 - 1,000 if playing on Normal.
Mr. Driller, Angry German Kid, and other platformers
The value varies depending on how quickly the player collects it. Each one is worth 100 - 1,000 points each, and the decreases by 10 points every 0.01 seconds. For example, if the item was laying on the ground for three seconds without being collected, it would be worth around 700 points.