Some of my apps will echo those already listed, but my most used apps are:
Weave - News/RSS reader, very quick to update even with hundreds of unread news items and formatting of articles is generally very good
ESPN - Not much to say, great sports app for checking scores and game highlights. My only wish is that they can add a Live tile/notifications or the ability to pin our favorite teams.
PrimeTV - Nice TV app to keep track of your favourite shows. Good Live tile which updates to your next episode throughout the week.
Carbon - Twitter client. I've used Birdsong and Mehdoh and found both nice as well, but I like Carbon the best for it's speed and features (in line images are cool).
4th & Mayor - Foursquare app, made by a MS employee and has better performance that the official app (although arguably not as nice looking).
WeatherMaster - Nice weather app. As far as I know it is the only app which has a GPS location that can follow you on the Live tile which is handy during the week where it will switch from my home to work locations automatically.
Parcel Tracker - Track delivery of packages from any shipping service with live tile and notifications.
MyStocks Portfolio - Stock tracking app with Live tile for my employers stock price (Free version).
Also, a few of my favorite games at the moment:
Wordament - Highly recommended, free and soon to be Live enabled as well
Price: $74.99 (HD) | $69.99 (SD) | Ignite TV $74.99
DTV can order on Nov. 21st & Ignite TV customers can order now!
Reigning heavyweight world champion Deontay "The Bronze Bomber'' Wilder takes on his most dangerous challenger as he defends his WBC title in a rematch against once-beaten Cuban slugger Luis "King Kong'' Ortiz.