Well if you are doing presentations then 5mW is the top power of laser you can use if there are people present in the room and if they are not all wearing laser goggles
There are a number of laser colors (wavelengths) that you could get in 5mW. Green or red would be the most common and inexpensive. Keep in mind that some green lasers can be "over spec" and therefore are not eye safe. This would be for example a green laser sold at 5mW but which actually puts out 10mW, 15mW or even 35mW for example.
You could also get a yellow (or other rarer wavelength) of laser pointers at 5mW, but this requires a more complicated series of steps to produce the yellow color and thus may cost you a few hundred dollars.
Laserglow.com has a 5mW green called the Galileo which can run continuously and will not be overspec and thus safe. In addition it will have an IR filter which will screen out any extra infra red light generated by the process which produces the green light.
The laserglow laser will be very high quality and should not let you down! They also have some other nice green lasers which are 5mW or less (class IIIa lasers)
Red is nice but don't forget that green lasers are closer to the peak of our sensitivity to perception of brightness of color so they are the most visible compared to other colors of equal mW power.
A wavelength of 555nm is the peak of our sensitivity within the visible spectrum so 532nm green is closer to this and is much brighter than 650nm red which is further away from this peak sensitivity wavelength.
Try this wavelength brightness comparison chart in the link below. Just enter some wavelengths and power in mW to compare brightness. In the calculator if you put 5mW red to 5mW green the red is only 12% as bright for the same power in mW.
A few common laser wavelengths in nanometers (nm)
650 red
589 yellow
532 green
473 light blue (closer to aqua blue)
445 deep blue
405 violet
Ya, green is a lot better for pointing. This is the first laser i ever got. Its a 5mW green laser off amazon. Got it for dirt cheap. Forgive the mess, bed bugs got in our bed last year so we had to move an air mattress in the living room. Along with all our cloths...