Extended/Full-Spectrum Photography

Here is a graph to show the general sensitivity of a sensor to various wavelengths:

By putting an IR filter over your lens, you were able to take pictures in the near-infrared range because the hot mirror is not perfect. You can do a "full-spectrum conversion" by replacing the hot mirror in your camera with plain glass. Then, in principle, any frequency from UV to near-IR can be photographed (Around 300nm to 1000nm, shown in the graph). You can use filters to isolate the frequencies you're interested in.

Use of Non-Visible Spectra

Although astrophotography and forensic applications most readily come to mind, there are other uses for extended-spectrum photography. For instance Blue+IR may be used to analyze vegetation.

There are sensors that are used to detect x-rays used in medicine, archaeology, and airports. X-ray crystalography performed by Rosalind Franklin (on film!?) was instrumental in determining the structure of DNA.

MRI machines "photograph" using magnetic resonance instead of light. Ultrasound machines do the same with sound waves to create "photographs" of the heart (echocardiograms) or a fetus. Blind people who use sound to "see" use the same region of the brain that "normal" people use to see with their eyes.

(Color) Filters

If you refer back to the graph, you will see that 400-500nm corresponds roughly to blue-green. B&W photographers often use color filters: Blue, Green, Yellow, Orange, and Red. But with digital cameras, there's not much need to buy colored filters anymore because they're pretty much built into the Bayer color array located over the sensor of your camera.

Although individual filters may not be too expensive (costs range from a few to a few hundred dollars, depending on the type of filter), it can add up if you choose to purchase too many. Unless you convert your camera to full spectrum, there usually isn't much need to buy many color filters. (Exceptions include IR, UV, didymium, ND, polarizing filters.)

Notes

• Obviously, your digital camera cannot record frequencies outside the range that the sensor is sensitive to (approximately 300-1000nm).

• Although some may not consider imaging of the electromagnetic spectrum outside of the visible range to be "photography", they do still involve photons.

• For non-electromagnetic energies, "photograph" is used as a metaphor. Hasn't anyone ever heard a kid being told about their "first photograph", the ultrasound from when they were still inside the womb?

• Reasons you might still want to use color filters, per @MichaelClark:

  When using a Bayer masked camera to do B&W work, use of an additional color filter in front of the lens allows one to increase the overall exposure without blowing out one color channel (that one would plan to reduce in raw processing anyway). This allows a higher signal-to-noise ratio using the wavelengths one plans to emphasize.

  Are there reasons to use color filters with digital cameras?
  Do I still need to use color filters for images that are to be presented in monochrome (B&W)?