Using your on-camera flash can produce pictures that are extremely blown out or that have extremely dark and hard shadows. When shooting indoors, lighting conditions are usually poor, so we tend to use flash on our cameras.
I shoot with the Nikon SB-700 (Amazon – link) and I love it. Nikon’s CLS (creative lighting system) is probably the best in the industry. A speedlight will take your photos to the next level and allow you to capture the moments you want, without the crappy harsh pop-up flash that is built into your DSLR camera. The flash head has a tilt and swivel mount so you can direct which way you want the light to bounce.
It uses 4 double AA batteries and can shoot around 200-300 photos before needing to replace them (just depends on amount of power you are using for your flash). I have also bought multiple sets of the new energizer AA rechargable batteries (Amazon – link) that work excellent.
Note: An excellent an inexpensive attachment that will help diffuse the light is the Sto-Fen OM-700 (BH-Photo link)
Compare these two shots I took of my dog in my living room within seconds of each other. One using the flash, one with the speedlight.