Salifert definitely seems to be the popular choice and I've never heard anything negative about their kits. I myself use Red Sea, which has always been accurate for me. My LFS (a guy I trust) says he uses Red Sea and they're comporable to the more expensive ones, very accurate.
I do plan on switching to Salifert when I run out of my current tests, though. Can't stand the peer pressure.
Something to stay AWAY from, though....I don't know if I just got a bad kit, but I purchased a calcium test kit by Aquarium Pharmaceuticals. It showed--twice--a calcium reading of 740 in my tank. I freaked out and took my water to my LFS, and it ended up being 420. So just a little heads-up on that one...