S/W or F/W? this is mainly for F/W..
You need...
Patience.
What type of fish and how many where you wanting?
First research the fish your wanting till till you understand them and their needs.
Know your tap water chemistry and how to adjust it.
Water chemistry test kit...
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=5364
Dechlorinator
Ammonia for a fishless cycling.
An firm understanding of the nitrogen cycle.
Heater...200watt
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=3852
Filter...AC 110 HOB filter or a canister type filter (ie fluval 203 or 303)
Lighting (depends on type of fish and if you are having plants)
Cover for the tank.
Suitable stand for the tank (to hold 500lbs+)
Substrate, plants, driftwood miniature castle or scuba diver etc.
Hose for syphoning tank water, 2 buckets (plastic 3g-6g).
More patience.
Dr Joe
.