The apps that i use almost daily are...
Safari ( but thats built in and for most basic stuff)
Atomic Browser (for all long reading and adblocking features and more web optimised websites)
GoodReader (for all my document management and PDF reading)
Ibooks/Stanza (for Ebooks)
Reeder (for all my RSS needs)
Pulse ( for a few photo related RSS feeds)
Adobe Ideas ( for sketching and planning in interior design)
Sketchbook Pro (more advanced features like Shading and elevation and simple sketching with layers etc)
Air Video (watching videos from my PC)
Digits (Calculator)
Todo (for task management)
All these apps gets used atleast once daily.
Plus a few indispensable ones like imdb, Howcast, epicurious / Betty crocker, wikipanion free, appadvice, radio.com/accuradio for my radio fix etc are also used occasionally!