If I could only pick one I'd have to say Twitter. I don't do updates myself, but being a big sports fan, I follow alot of my favorite reporters. It's great to get their insight during games and I also find alot of breaking news on Twitter before it makes it to TV or online.
Other than that? I like Wunderlist. I can constantly update it from my computer at work or at home, which is useful since I try to go shopping only once a week. So essentially for me it is a glorified shopping list. Pandora and Wolfgang's Vault are great, and I have a ton more, but I'm eager to use "My Fishing Advisor" when it gets warmer out and I go fishing. I just wish the GPS worked with it, which it's supposed to be doesn't seem to.