Laser pointers are handy sources for coherent light. The green and blue varieties are actually diode-pumped solid state lasers, all in a hand-held package. The IR wavelengths used for pumping are typically left in the beam, so your green laser pointer is actually a fairly bright IR laser with some green thrown in.
This was discussed in a NIST technical note (arXiv). Here’s the spectrum for a green laser pointer they measured. Note that it’s way hotter in the IR than in green.
Besides imaging and aligning optics (and, apparently, pointing), they’re useful for demonstrating different physical properties of light.
I rather enjoyed rpg’s post on using a laser pointer to investigate the wave nature of light. Key quote: “So the wavelength of my laser is about 500 nm. Seeing as it’s rated as 532 nm and I’m a biologist, I’d call that a result.” The basic idea is to replicate Young’s classic double-slit experiment using a laser pointer as the coherent source.