HotKey Resolution Changer is a tool which can change your screen resolution with a keypress.
Launch the program and it initially displays two shortcuts. Each of these can be assigned a resolution, colour depth (maybe), refresh rate and hotkey. Minimise the program to your system tray and it'll switch screen resolutions whenever a hotkey is pressed.
If two resolutions aren't enough, right-click HotKey Resolution Changer's system tray icon, select a higher value (anything up to 9), and define each one to suit your needs.
In theory, at least, you should be able to set up a shortcut to rotate the screen by 90 degrees, sometimes useful for reading text. This didn't work for us, but perhaps it was a display or display card issue. We were also using the program on Windows 8, which isn't officially supported.
The other setting is a "raw mode", which allows you to set your system to any mode supported by the graphics card, regardless of the monitor's capabilities. This might be helpful, but it can also cause various odd problems, so avoid it unless you know exactly what you're doing. And even then, make sure you remember HotKey Resolution Changer's emergency hotkey, Ctrl+Alt+Shift+R, which restores your initial resolution if there are any problems.
We had a few small issues, but in the main HotKey Resolution Changer delivered on its promises, changing our screen resolution on demand while consuming minimal resources (3.1MB RAM, typically). This didn't happen instantly on all our test PCs - switch from low to high resolution and it sometimes takes a few seconds to repaint - but that's normal. If in any doubt, try switching from the standard Windows display properties and watch what happens.