This isn't just the best Google Reader app we've found; it also has one of the nicest interfaces we've seen in a Windows 8 app. You can see your list of feeds, the stories in one or all your feeds and the selected story on screen all at once in a view that still manages not to look crowded (and tapping the story loads the original web page into the story pane very elegantly). Or you can flip into a tiled view with no interface, just headlines and pictures for a quick overview; tapping a tile brings up a half-screen pane showing the story in an interface that defines clean and clear. Plus it syncs well with your Google Reader account so you won't find yourself reading the same stories again on other devices.
Ribbit and Narwhal are both worth a look, but the best Reddit app for Windows 8 so far is ReddHub; you can even use it without logging into Reddit if you want to see the cat pictures without joining the debates. You can pin subreddits to the Start screen, submit and reply to links (with decent quoting) and use the Share charm to send links to Reddit or share links from Reddit but perhaps the best feature is the way it automatically resizes pictures to fit on screen. We've never thought of Reddit as beautiful but that's what ReddHub is. Also, prepare to lose hours reading…
If you want to explore random Tumblrs or follow one in detail, Single Stream has a nice interface for doing that. But if you want to manage and update your own Tumblr as well as reading the Tumblrs you already follow, Tumbukun is a good – if rather primary coloured – app for that. You can like and reblog posts and write your own posts from scratch in the editor, although if you want to end an existing post you have to open it in the browser (annoying if you spot a typo right after you post).
The Messenger client for Windows 8 is very purple and uses a lot of space for just Messenger (and linked services like Yahoo and Facebook Chat). If you use other IM services, grab a copy of IM+ which covers all the main services including Google, Jabber and ICQ as well as the ubiquitous Messenger, AOL, Facebook, Skype and Yahoo plus international ones like RenRen and Yandex. The interface is fairly stark but there are plenty of handy options from blocking people you don't know to getting email alerts for messages you miss when you're offline.
The Windows 8 Skype app merges Skype and Messenger (and your Skype and Microsoft account); you see recent calls and chats made on multiple Skype devices, your favourite contacts and people you've talked to recently – or you can see your full address book as tiles. Plus you get Skype as another way to contact friends from inside the People app. If you prefer Google Voice for calls, check out Freetalk.