True Calendar 8The native WP8 calendar sucks, it defaults to viewing one day, but doesn't fit it onto one screen, it doesn't have a week view at all, the month view is pretty much useless because you can't read the appointments and if you try to click on them or click on a day it switches to the crappy day view.
I can't recommend True Calendar 8 highly enough, it possibly has too many configuration options, and you can only have a maximum of one account each of Google, MS and Facebook, but apart from that it's pretty much perfect and is what the native calendar should have been.
Ocell (Twitter)Ocell is buggy, crashing and refusing to load tweets relatively often, however in my experience, and given my demands, it is still by far the best WP8 Twitter app that I've seen. My demands mainly being configurable, swipeable columns, mainly consisting of my lists, just like Tweetdeck and then Hootsuite let me do.
Another option is Flickr Booth. It does all of the things that I like Flickr Central for, and beats it with its simpler interface, ability to choose to auto upload from all photo albums and contacts' upload page, which is the landing page and shows more than one upload for each contact. However the auto upload function seems buggy at the moment.