XBOX MUSIC... If you're a music lover, how could you not take advantage of accessing a majority of the music ever published for free at CD quality? It beats the hell out of Pandora and Spotify.
Modern IE for the majority of my browsing, but definitely not development.
Mail and calendar apps, most of the time. All I usually need to do is read, reply, and delete or move to another folder, and the mail app makes it extremely easy and quick to do those things. I also like having the notifications and lock screen summary data, The weather app isn't accurate enough for me (I use the NWS NOAA website), but I do like the radar display.
OneNote, I use all the time. I don't ever use the desktop version of OneNote 2012 anymore.
Photoshop Express for simple cropping, and brightness/contrast/hue adjustments. I do this a lot, and it's easier and quicker to do in this simple setup than in Photoshop.
Also, a lot of content apps, like NBC News (which has all of their news programs in full for streaming in excellent quality), Kahn Academy, Stanford videos, etc..
Twitter, not that I tweet often, but their app is much better than the website, as are the apps for most web services.
Oh yes, and Skype.