New 28 gallon nano cube

If you've never had a saltwater tank or experience with one prior I'd suggest doing a freshwater nano cube, reason being is you have a smaller volume of water which leaves basically NO room for error and with saltwater it's more finicky in my honest personal experience.

But as far as what you'll need..it's basically the same as a freshwater setup and depends on how advanced you want to get and what you plan on keeping within it.

*Lighting (depends on what you plan on keeping).
*Canopy (optional, but definately a plus to keep evaporation at a minimum)
*Thermometer- to see if your water temperature is fluctuating, if it is...that brings me to the next item
*Aquarium Heater- Submersibles are easier to hide
*If your not doing a bare bottom setup then you'll probably want substrate such as aragonite
*again, depends on what your doing...but I'd suggest a couple pieces of live rock (cut eggcrate/lighting diffuser to fit the bottom of your tank to help with the weight, then place your live rock, and then your substrate). There's a reason for this order..it's so your live rock is more stable and doesn't shift when/while doing partials. People have also drilled through the rock and configured it with white PVC like you find at the hardware store and have even used Zip Ties, but being a small tank I'd doubt you'll be wanting to do any of that (or need to for that matter).
*Refractometer - to measure the amount of salt in your water/mix
*Saltwater Aquarium Salt
*Full Saltwater Test Kit...to monitor the tank for "cycling" and in case any issues appear that's the first thing that anyone will ask you (water's parameters).
*Protein Skimmer (optional some will say), but I recommend them. (dependant on the type purchased you may or may not need an air pump and airstone).
*Saltwater approved filter (but if enough live rock is used, that can be used as a natural filtration system).
*Possibly a powerhead or powerheads (to prevent dead spots, anywhere your not receiving circulation).
*Additives (again, depends on what your putting in the tank) such as limewater/kalkwasser, Seachem Prime, etc.
*RO/DI (optional) unit/system
*Siphon for doing routine partial water changes
*nets, algae magnet/scraper, notebook for keeping track of parameter and routine maint., bucket-heater-airstone: for pre-mixing saltwater to top off the tank or replace siphoned water.

 

if your not sure what you want to do with the tank, I'd suggest going somewhere like Barnes and Noble where you can sit on a couch and read the book BEFORE being forced to pay for something that doesn't help you....take a note book to scrawl important information.

A good site to look over when considering stock would be somewhere like http://www.saltwaterfish.com/

 

and here's a few other good links that may prove helpful.

testing and parameters--> Understanding Marine Water Testing & Parameters
a few online saltwater retailers--> List of Online Saltwater Retailers

 

Your most welcome, and I wasn't sure about the saltwater experience so I figured I'd cover all the bases just in case