It has been a bit over a year since I tossed paper and went with the iPad. I now use my iPad with stylus at all meetings and brainstorming sessions. I also regularly use it to check a project status and read documentation (with Safari and SharePoint), and occassionally to unwind with a movie. Below are the apps that I use and recommend.

Productivity:

WritePad // Natural handwriting notes with Boxwave stylus. I spend about 70% of my iPad use in this app.
Adobe Ideas // Whiteboarding ideas. I spend about 15% of my iPad use in here.
SharePlus // Requires SharePoint, but a great way to get documents onto the iPad securely. 10% of my iPad use.
OmniGraffle // Flowcharting app
iThoughts HD // Mindmaps app

All Purpose Calculator // Handy because it keeps a running tally of your operations.
Dropbox // A great way to get documents onto the iPad if you do not care about security.
Logmein // Remote control of computers, requires a LogMeIn account.
WinAdmin // Windows RDP client that supports multiple connections
TouchTerm SSH // Linux/Unix terminal over SSH

Reading:

Google Books
Kindle for iPad
Nook for iPad

Relaxation:

All the games from Optime Software // Chess, Checkers, et cetera,
Brushes // Painting app that works well with a stylus
NetFlix // Videos onto the television using a Apple composite AV cable
Supremacy Wars // A game my daughter and I have been playing
Songify // For creating auto-tune songs

Others that people have recommended to me:

Evernote // Popular with my team, but I like WritePad better
Instapaper // Popular with the Lifehacker set, but I like Viigo on my BlackBerry