Skydiving in the territory is awesome! The views are fantastic, and it will be an experience you never forget.
A tandem jump costs around between $290 and $350, depending on the height you jump from. I highly recommend you fork out the extra $$$ and jump from the highest altitude possible...the freefall is much longer, and more enjoyable. If you have a spare $100 - $120, I also recommend you get a video of your jump...its great for the memories, and to show off when you get home!
There are two companies that do tandem jumps around Darwin, TopEnd Tandems and Skydive Territory.
I know people who have jumped with both companies, and both come highly recommended. TopEnd Tandems leave from Darwin Airport, so are easily accessible from darwin, their jump zone is over Lee Point Beach.
Skydive Territory is based in Batchelor, 80kms south of Darwin, at the gateway to Litchfield National Park, so if you're heading down to Litchfield or Kakadu, its definitely worth the detour. They jump over Litchfied National Park, Lee Point Beach, and other places inbetween.
Contact details for each are as follows:
Ph: 0412 442 745
Ph: 0417 190 140