Ammonia, Nitrite, Nitrate, Phosphate, pH (high range), Alkalinity. If this is a reef setup, you also want calcium and magnesium kits.
I'd go with SeaChem, or Salifert. Skip the dip strips...they can be accurate enough for a freshwater, non-planted setup, but for anything else you need better accuracy. Plus the strips will go bad if they are stored improperly.
Former advisor and planted tank geek...life's moved on though.