Look, I'm a big fan of Flipboard... But it has no place on a watch. I can see Steam for chat applications or whatever, but seriously, Flipboard? How would that even work? Would it show headlines only or full stories?
I guess you can count me in the camp of "the watch has its own special purposes and some apps are best left on the phone/tablet."
That said, RunKeeper, Strava and Wahoo are my fitness trio of choice for the Apple Watch.
I'd say Honeywell for their smart thermostats (or Nest if you've got it), but their iPhone app leaves much to be desired (IE: login every time you use the app) so I'm not thinking a watch app would be particularly useful.
It's a stretch, but there's one awesome app which I would love to have on the watch: Just Landed. For those who don't know, it's a flight tracker which looks at your location, traffic and flight delays, then tells you when to leave so you can pick someone up at the airport. My only complaint is that it should do the same for when to leave to drop someone off too, but seriously it's a great app. Being able to check my watch and it gives me an accurate countdown for how much time I have left would be an amazing improvement from simply checking the time. Actually, I wish I had an app that did that for literally everything. "Oh, my pizza will be ready exactly when I arrive if I leave in five minutes? Cool." "Hey, we need to leave in 17 minutes if we want to get to the theater when the doors open." Etc. Sure, you can check the map, get a travel estimate, plan ahead how much time you need, check the map again when you want to leave and keep adjusting your timing, but why not have an app do that for you?