SeaChem and Salifert are what I recommend for a decent balance of quality/consistency and pricing. However, LaMotte is very good quality (with a price to match). As far as what specific tests you should get:
ammonia
nitrite
nitrate
pH
Then, depending on budget, source water, and what you're planning on keeping I would add:
phosphate
alkalinity/hardness
calcium
A good quality hydrometer or
refractometer should be considered part of a good test kit, I hate swing-arm types myself, though others like them just fine.
I also absolutely LOVED having an O2 test, I cannot for the life of me remember the brand, but my favorite (and the only reliable manner in which to test, AFAIK) used little vacuum vials. I would submerge it in the sample (which I harvested mid-tank, with empty container submerged til at level, then opened, then closed under water), then break the vial, it would suck in the water and give me my saturation levels. When I first used I didn't think it could really give me any "variety" of reading, but it did. I liked it for sumpless systems and displays that were a bit tightly sealed with regards to canopies, etc. Nowadays I see little need for an O2 test, except for fun (especially when observing the difference in saturation of water of different temps).