One of the best accessories you can get from Santa is an external flash.
If your camera has a hot shoe on top or is a DSLR, chances are it can handle an external flash unit.
So which one to buy? I highly recommend buying the flash unit that’s manufactured by your camera manufacturer. Yes it will be more expensive than a no-name brand but it will work better. And, when it comes to buying the tiny external flash or the more expensive medium size one or go all out and buy the big really expensive flash, well the decision is up to you.
What size flash will determine how much light you can throw on your subject. And with an external flash that has a pivoting head (not all do) you can point your flash at the ceiling or side wall or into a reflector or umbrella for much more pleasing photos than direct (read ugly unless you’re using your flash outdoors as a fill light). If you’re going to bounce your flash, you’re going to appreciate having a bigger flash that can throw more light around.
If you’re shooting the kids in the house a smaller unit will do. If you’re shooting weddings or parties held in big ballrooms you’re going to want a BIG flash. I’ve got two SB-900s and am considering buying a third one. With two flashes I can set up a portable studio anywhere with two umbrellas and using the Nikon wireless CLS system control them from the camera. This is unbelievably cool. Canon has much the same type of system as well.
This setup can rival full studio setups with monolights (those big expensive ones that pros use). Now would I like a pro setup with three monolights (main, fill and one on the background). You bet (and bigger is better again) but I don’t have a place to use them. If I was doing lots of portraits I’d want a studio with really high ceilings. But most of my portraits are done in business or home offices with regular height ceilings. The two SB-900 speedlights on umbrellas with a black or grey background works perfectly.
The website Digital Diversity has an excellent article on Why you should own an external flash which is good reading.