If I'm not at my Mac then I'm usually within arms reach of my iPhone or iPad. Trying to maintain a GTD mindset is an important goal for me, here are 5 productivity iOS Apps I'd recommend with links to them on the iTunes store.
(In no particular order but I have made both UK and USA App Store links available)
1. Daylite 4 & Clear (ok that's two Apps - but Daylite is not for everyone so I wanted to present an alternative)
Daylite 4 by Marketcircle is a full project management system which allows me to view client details, create opportunities, projects, tasks, notes and track pipelines project stages. I use it heavily and it's the heart of my productivity - but it is 100% reliant on having the full business product on your Mac (which I know is not for everyone). For more information about Daylite you can visit the developers website or to download the App click on the link below
Clear by Realmac Software is a VERY easy to use, simple system that user gestures for interacting with your tasks. Check out my review here. It's great for getting things done and staying on top of your tasks.
2. Remote VNC
Remoter VNC is a fantastic App that allows me to remote log into my computer and access everything as if I was sitting there in front of it. It works with Windows, Mac's and Linux computers.
Apple's Pages App is Apple's answer to word processing. It's simple, easy to use and connects to your Apple iCloud account so you can sync your documents between iPad, iPhone and Mac. It even supports Microsoft Word documents. This means you could be on your way to the office and start a document on your iPad then finish it at your computer when you arrive. But even if you won't use that feature - Pages is a must for Word processing on your iOS device.
4. PDF Expert
PDF Expert by Readdle is essentially 'Acrobat' on the iPad. It allows you to manipulate PDF's, fill out electronic forms and sign files digitally. I use it most for opening a PDF / screenshot of a design I may be working on and then making marks/sketches over it using the iPad touch screen.
If you don't know about Dropbox yet - where have you been?! Dropbox is a free service that lets you upload photos, docs, and videos to a private online account and share them easily with yourself (on the move) or others. Ever emailed yourself a document? With this you won't need to, access your files wherever you are. Because it's free I'd recommend signing up and giving it a go - you probably won't regret it.
Visit Dropbox and signup for free (you can then download the App)
I hope this list is helpful, feel free to add your suggestions for productivity Apps in the comments below.