First, get a piece of paper. Heres some of the things you need, and you NEED to write down the cost. Doing a saltwater tank, especially a reef tank is a slow, slow, (did I say slow?) process. Its not like FW where you buy something nice in the store, throw it in, and watch it. SLOW.
You will need the following, and this is just a partial list:
GOOD lighting. A regular hood will not cut it. You need either power compact florescent lighting (cheaper, less heat, but less options for corals and clams later on) or metal halide lighting (expensive, hot, but the best you can get for a reef tank.) Start looking on ----, hellolights.com, or the many other sources out there. Remember, write down the cost.
Filtration: there are 3 different filtration needs. Biological, mechanical, and chemical. In a reef tank in my opinion, you can do the mechanical very easily. Mechanical filtration is the removal of particles and waste from the water. Its usually the only form of filtration in FW. For our reef tanks we use Aquaclear filters with JUST the foam pad in them. Does a great job, cheap, and quiet. We use an aquaclear 300 on our 54 gallon reef, and an Aquaclear 500 on our 90.
Chemical - this is strong stuff, read up! You need excellent and stable water conditions in a reef tank. You must learn what you need to monitor, including ammonia, nitrate, nitrite, PH, ALK, calcium, phosphorus and specific gravity, salt content. You must learn about the cycle a new tank goes through, and how to determine when its complete. For chemical filtration, a protein skimmer is a common choice. I use a refugium, which is simply another tank (much smaller) which my water passes through, filled with live rock (which offers many forms of filtration) and miracle mud, which replentishes trace elements and helps stabilize the PH of the water. On one tank we use an ecosystem 60, which accomplishes both chemical and biological filtration. Biological is the creation and maintenance of bacteria which feeds off the 'bad' chemicals your creatures will create. A popular and highly recommended method of biological filtration is a Deep Sand Bed, or DSB. This theory portends that a sand bed of 4" or more will have anaerobic (no oxygen) areas that host bacteria that specifically removes ammonia, and nitrates. Again, read up.
Live Rock. Filtration, good looks, and introduces many creatures into your reef you could never hope to put there manually. Also has some dangers, read up!
Sand.
Salt. I use Instant Ocean, I recommend it.
Buckets.
Cleaning and manipulation tools, like algae scrapers, sticks, claws, etc.
A hospital tank. A smaller tank set up to duplicate the conditions of your main tank that you can use to quarantine new fish, and treat those that get ich, or other problems.
A good refractometer, and test kits. (A refractometer is a device for measuring the salinity in the water. A hydrometer is a cheaper, less accurate device for the same thing.
Powerheads for water movement. Water in a saltwater tank should be zooming all over the place, especially in a reef tank. Read up for more on this, but in a basic 50 gallon setup I think you want at least 3 small (150-200 GPH) powerheads swirling things around.
Ok, I probably left a few things out, I'll check back in a bit, but this should get you started!
you have come to the right place. i am new here as well so not really going to give you advice as far as specific equipment, dont know enough about them myself. first you will need to decide if you want to have a fish only, a fish only with live rock, or a reef tank. post on the various boards here and ask questions to help you decide this, from there you will need to get filters/skimmers and such. these things will change some as you decide what you actually want to do with the tank. for example a fish only tank will not require near the lighting that a reef tank that will have very light sensitive corals in it will. dont worry though it will be easier to make this decision now and get the right equipment than it was for me to change your mind in mid-stream 
