A quality flash is an essential piece of photo equipment; and today’s flashes are both extremely sophisticated and user friendly. I have a different tack, though.
As a beginner I think that you would get more use and have more fun using the $240-270 you would spend on an external flash by upgrading the lens. Either to something a stop or two faster, but most likely by increasing the range of the zoom. Nikon makes an 18-200mm f3.5/5.6 that allowing for the digital conversion would give you something in the way of a 29-320 mm lens. That is a lot of versatility. What you would lose in the super wide range you would more than make up for when it came to normal perspective shots, portraiture, and telephoto capabilities (your kid’s sporting events, a grizzly bear on the family vacation to Glacier National Park, girls at the beach if you are single).
The D50 has a pop up flash that is metered for the camera. And, while it won’t pop out a crap full of light like some of the bigger units, it will do nicely for fill work and distances up to about 10 or 15 ft.
Zach is a professional photographer and his portfolio speaks for itself. I couldn’t agree more that a quality flash will improve your work, but as a beginner and someone who might be looking to take pictures for an album or to post on the internet I think you would get the most use out of a lens with greater latitude.