Thomson is the standard regurgitated anwer to this question. Yes, they're strong, yes they're good, but so are a lot of others. The Thomson Elite is definitely a nice stem, but it's beefy. Not heavy and pretty fugly because of its bulk. A lighter, better looking option is the Thomson X4, but that's only available in a 31.8 bar clamp size.
If you're looking for lightweight and reliable, I'd also consider the Race Face Deus mentioned earlier.