I use Salifert kits myself. I've seen numerous tests by people with access to lab grade test equipment, and the Salifert kits have always come out well. Hach and Elos test kits are also reputed to be very good, although I've never used either of them.
I test for:
Alk/Dkh
Ca
Mg
pH
Nitrates
One thing to keep in mind is that test kits will go bad after an extended period of time. I had both a calcium and Alk/Dkh kit start to give bad readings recently. I have 170 gallon system with a Geo calcium reactor. The Dkh and Calcium levels started reading off when they had been good. All other parameters were fine, the reactor was working fine and was set as it always had been. Re-testing with new test kits showed levels in line with they should have been. My calcium levels were up by 70 ppm from what the old kit said,(460 vs 390), and the Dkh was up 2.3 from what the old kit said, (11.5 vs 9.2).
Moral of the story is to label when you open your test kits and consider throwing them out/replacing them after 9-12 months....
Like Herefishyfishy said, the test kits you will need will depend on what type of critters you will be keeping. If you're not keeping corals, you shouldnt need calcium or magnesium kits.
Nick