Thus far I've been ok with just hostgator; but I haven't launched a server crashing product... at least not yet

One of biggest marketers on the WF recommends "cloud hosting" though I forget the actual name of the hosting service. Might be worth looking into cloud hosting in general just to see what it can do for you.

By the way, S3 is great; just not sure it falls under a "host" per say; as from what I understand - S3 is pretty much a barebones storage space.