I will got a lot of flack about this one, but here goes….
Don’t buy a flash in the beginning. Learn to use the camera to its’ full potential and then look into a flash or other light source for your work. Exception, if you are going to be doing mostly people photography…in that case, you will need a flash or other light source from day one.
I am a landscape photographer and I use a flash well less than 1% of the time. In fact, I have to get the manual out every time I use it, because I forget how to use it after months or years of not using it. I do light things up with a flash light or a hand held flash not attached to the camera or use a reflector to bounce some light from time to time…but that is kind of advanced stuff I won’t get into it now.
If you are just starting out in digital photography…you have your hands full just learning the camera and the editing tools. Work on those first and add flash photography once you have mastered the basics.
Aloha.