http://www.facebook.com
It has always delivered a clear message: you must have an account to use this service.
It's great for FB but would be horrible for just about any other product or service.
When I look at that, I think "Worst landing page ever...what the hell does it do, why should I bother, and how do I get it?" But then, if I have to ask those questions...I've probably missed the point, and SnapChat would be useless to me. The whole point is for it to spread virally, so a landing page is pointless.