Theres meant to be a supplement in The Sunday Business Post tomorrow so that might have more but these are what I use.
Documents (free version or full version) it basically opens all forms of documents. I know its small on the iPhone but it does help to be able to open attachments on the go.
Dragon Dictation (free) I use this all the time. It converts speech to text and is far more accurate than you would think.
Quick Voice (free) or Voice memos (free) there are other options as well but this is the one I use basically a Dictaphone. I have used digital Dictaphones but the clarity on this is much better.
XE currency converter (free) does what it says
Twitterific/wordpress/facebook (if your business uses those)
App box pro (free or full versions) basically has a load of basic apps under the one roof for example calendar/calculator mail. I know with folders on the iPhone now this doesn't make as much difference but its handy to just open it up and see them all there and there is less clutter
Dictionary (free)
Free translator.
Adobe ideas (free) basically if you think of something you can get it down there fast.
Instapaper (I can't remember I think this is paid) - allows you to save online documents to read later. So say you are travelling and may not have 3g/wifi
Twin web- allows you to browse two websites at once. It splits the screen.
Therea are loads more what area of business would you be using it for generally so I can have a look and see what I can find. I have too many to list
ETA iePhonebook basically a golden pages for your iPhone