I have an LCD screen which expects power from a 5V line, but I want to hook it up to my Raspberry Pi's GPIO pins which only supply 3.3V. What equipment do I need to increase the voltage from 3.3V to 5V?
If you only need to send data to the LCD you can use HCT buffers. HCT is TTL-compatible HCMOS, so made to work at 5V, but instead of needing 0.6 Vcc input for a high level (or even 0.7 Vcc) it can do with TTL levels, i.e. 2.4 V for a high level.
The 74HCT241 is an octal buffer.
For status and other unidirectional lines from the LCD you can use a resistor divider to scale the 5 V down to 3.3 V. A 10 kΩ resistor in series with a 20 kΩ gives you 3.3 V out for 5 V in.
If you want to interface 5V and 3.3V logic you will need a level shifter. Maxim has a good app note on this here: http://www.maxim-ic.com/app-notes/index.mvp/id/3007
For I/O lines make sure your chosen level shifter is bi-directional.
You will not be able to power your 5V LCD from the 3.3V Raspberry Pi without something like a boost converter, or use a separate power supply.
This question was researched by user pygmalion on the RPi forums, and the findings were that for some LCDs, there is a way to switch them between 5 V and 3.3 V logic and between serial interface and parallel interface on the back side of their PCB (source).
This includes JLX LCDs based on the ST7565 LCD controller and sold on the Aliexpress.com site. When you have to indicate which logic voltage you want, it seems to be an indicator that the device will be configured by the seller before shipment. I just looked, and still found such LCDs around (example). Maybe yours also has this capability.