Hum, things I'd get to set up the tank:
-- Good quality sponge filter with an air pump to run it. I just like them better than HOB filters, but it's preference. Sponge filters can hold a ton of good bacteria and are very quiet.
-- Submersible heater, rated about 50W. Splurge on a better heater. Cheap ones tend to break and have unreliable thermostats.
-- If you want to go for gravel, fish seem to look the best on dark blue or black gravel. Only need a small bag. Just enough to coat the bottom of the tank with a thin layer.
-- Lights: you could get a light hood, but it might be cheaper and look nicer to get an inexpensive lamp from Target or Wal-Mart, a plug-in timer, and a compact flourescent spiral bulb (something rated equivalent to a 100W or higher regular bulb). Set the timer for 8 to 10 hours of light per day.
-- Dechlorinator: Prime is good, but almost any brand will work fine. Beckett Pond brand dechlorinator is pretty cheap at Home Depot, and works great.
-- Liquid test kits: Tetra brand is pretty easy to find, and not too expensive. Need one for ammonia, one for nitrite, one for nitrate. PH and other kinds of tests if you want them, but not strictly needed. The liquid tests are much better than the paper strips, and less expensive per use.
Beyond that, I guess it's all preference for fish, decorations, live plants, things like that. The stickies and the search function for this site are really useful for finding the steps to take to cycle the water and to stock the tank with fish.