If you are looking for a sealed headset kings are very good, but they cost absolutely loads. If your looking for a sealed headset for cheaper an FSA Pig DH Pro is a good option, its really good value for money andis really smooth (im using one right now). Some people say that Cane Creek S3s are good, but i havent really got an opinion on them as i havent ridden one but they are apparently a bit lighter than a dh pro and a bit more expensive, but i have also heard they can brea quite easily.
A good unsealed headset is an fsa pig unsealed, unsealed headsets tend to be cheaper than sealed and are usually a bit faster, but can get noisy and tend to break quite quick compared to sealed.