Adobe Reader There are times when I'm on the go but need to take a look at a document, or download a restaurant menu. Adobe reader app is very handy to have, and I like that you can leave notes and share them with collaborators.
AK Notepad You never know when inspiration is going to hit, and although I carry a journal usually, I don't always have it. AK works great for jotting down thoughts, ideas and reminders, plus you can share them via sms or email.
Springpad Springpad is a note taking app on steroids. Totally dig it! You can save and organize many different things, from websites to snap shots and personal notes. Great for collecting research or just saving yummy recipes.
ASTRO File Manager / Browser Incredibly useful app for organizing all of your photos, files and music. I've been able to clean up my phone of all my stuff by saving it in Astro's cloud system. Totally feel my important files are protected.
Hojoki - One client for apps Dropbox, springpad, evernote ... on and on, I use all of them. Hojoki helps me bring it all together into one spot. It's like the one app that rules them all...