We have build an enterprise iPad App and now we want to give it to our employees. Initially when testing, we used ad-hoc distribution collecting all the test device\'s UDID
There are two solutions
Try testflightapp.com
It does everything for you. It even has a SDK which I found very useful in debugging scenarios with logs and crash reports.
If you are looking to have your own hosted solution for the enterprise then http://hockeykit.net/ is the best bet.
It has a client application which makes the upgrade process painless. It also have a server side code which you can deploy on your server.
https://github.com/TheRealKerni/HockeyKit
Update 2013-11-23:
We have been using Diawi happily for quite some time.