tank
salt mix (ie. Instant Ocean etc)
Hydrometer or refractometer
test kits (ammonia, nitrite, nitrate, ph, alk for starters)
thermometer
heater (approx 150 w to maintain your temp)
powerheads (preferably 2 that will give good water flow say 2 Korallia 2's or maxijet 1200)
lighting sufficient for what you want your end result to be. (ie. if you are planning a reef then spend the money now for good lights you do not want to be upgrading lighting as it is expensive)
protein skimmer (don't skimp here get a good one such as an aqua remora C)
ro/di water don't use tap water
substrate, don't use crushed coral but use good quality calcium aragonite sand, the finer the sand the less you will need but aim for at least 4 inches
live rock, good cured liverock or you may cure it yourself, either way count on a minimum of 1 to 2 lbs per gallon. Yes that would be about 100lbs ideal but if you are using good rock from say fiji/marshall islands you could get away with less such as 60lbs depending on the porosity, the more porous the less you need.....
once you have all this set up......which is another whole list......
this is a great website with loads of information.
WetWebMedia-Marine Aquarium Articles and FAQ's