Here is a list of the apps that I've installed that I think are great for the N8. Feel free to add some that deserves to be installed.
I will try to keep the list updated every two weeks when more and more apps are released for the N8.
TunieWiki - Great Music app for media on your phone. Provides lyrics and a search on youtube feature. I found some bugs when trying to type in landscape when creating the account but after that ran smooth.
Soundtrckr - Great Internet Radio app. Just like pandora but provides extra social features like twitter and ability to listen to your friends stations.
AccuWeather - Great app for weather. Can be good for one of the home screens as a widget.
Fring - Great Video chat app plus more.
Skype - Great to make cheap international calls or free Skype to Skype calls.
Battery Monitor - Provides more detail for your battery status.
Opera Mobile - Very fast browser.
Swype - Once you get used to swyping then regular typing seems so slow and primitive.
Angry Birds - This is a must.
NFS Shift - It's free what more can you ask for.
GT Racing - The best racing game for the N8.
MathsBrain - Very nice app for you brainiacs. My best is 80 secs. Beat That!