During cycling you'll want Amonia and Nitrite. After you tank is cycled I'd say you can't live without Calcium, Alkalinity, Nitrate and pH. Use a glass floating hydrometer (sheaper) to check specific gravity (temperature dependant) or a refractometer (more expensive) to check your salinity (not affected by temperature). You'll want a good quality glass thermometer.
You will probably save money by buying only the kits you need. You will save a few bucks by buying a Tetra Laborette http://www.arcatapet.com/item.cfm?cat=573
. Here it's only $17. I used it when I was starting out, it is pretty good. pH, Ammonia, Nitrite, and hardness (Alkalinity). It also comes with a FW
hardness test that you won't need.
I like TropicMarin Ca
test. High quality.