Nice thing to start off with is fancy goldfish. Hardly (if any) temperature/water maintenance.
55 is big. You can put a ton of fancy tailed guppies, swordtails, mollies, and other live bearing tropicals.
It so hard to say what you should start with. Having a 55 gallon, you can start almost anywhere, from the aforementioned fisn to Arrowanas, Discus, Oscars...I can't even start.
Salt water used to have the rep of being to hard to maintain. This has gone by the wayside with new techniques and technology. Saltwater is still expensive. Unless you want to start with a few damsels.
To give you specific links? Nyahh. Type 'aquarium' at any search engine.