Apple announced last week that it would begin offering volume purchasing for iOS apps, and a week later the program is open for enrollment (but still U.S.-only, unfortunately). Enrolling in the program requires that you be authorized to make purchases for your company, and you'll also need a valid D-U-N-S number.
Volume purchasing allows businesses an alternative to the App Store for bulk purchases of iOS apps. All paid apps in the App Store are available through the program, at the same price as that listed in the App Store. Note that Apple's guide to the program doesn't mention anything about discounts for bulk app purchases, so purchasing Keynote for all 50 of your employees is going to run you close to US$500.
Custom B2B apps are also offered, allowing a level of customization and privacy not offered through the traditional App Store purchasing route. The program also simplifies bulk distribution of iOS apps, allowing distribution of purchased apps' redemption codes via email, an internal website, or third-party Mobile Device Management.
There doesn't appear to be any cost to enroll in the program, and it seems to be pretty close to addressing most of the features businesses interested in volume purchasing have been asking for since not long after the App Store's debut.