I travel about 80% of the time for business and rely on mobile applications for productivity while on the road. I have tested and researched many mobility applications for the iPhone and iPad and came up with the following list for those looking to minimize the need to carry around a laptop:

iMExchange2- App for keeping tasks and notes in synch with Outlook Exchange across adevices.

Evernote- Use for keeping meeting notes and documents organized, easily accessible, and in synch across devices.

DropBox- Best cloud storage application I can find, and I’ve used a bunch, including MobileMe.

Print n Share- Application for printing documents directly from your mobile device. You do not need to be on the same WiFi network to do so as it works over 3G.

JotNotPro- Use for scanning via a mobile camera, converting to PDF, and emailing. Eliminates need for scanner and fax.

Jump- Easy remote screen access to PC or MAC.

QuickOffice– Office applications for the iPAD. Compatible with Word, Excel, and PowerPoint. For iPhone, DocsToGo is best I have found.

EasySign (not primary recommendation, see below) Use for signing or editing documents in most common formats, including PDF and MS Office. Alternative to computer/laptop PDF editor (such as Acrobat) and eliminates need to print, physically sign, and scan/fax.

Docusign- Ink does everything EasySign does, and more.  Also, It’s a free App.

Penultimate– Eliminates need for pad and paper. Enables digital storage and filing of handwritten notes on iPad, and conversion to digital format, including PDF. Alternate App: NoteTaker HD

Xpenser- Great for expense management.  No need to save receipts.  Quickly record your expenses, snap a picture of your receipts, add notes, and later generate electronic or hard-copy customized reports.

Note: These applications were tested and used on an iPhone 3GS, iPhone 4, Macbook Pro running Snow Leopard, Lion, Mountain Lion, and a Dell Latitude E600 Running Windows 7 Pro. I purchased them all on the Apple App Store. I expect many would be available on Android, RIM, or Microsoft App Stores.