Yes, ahdoc distribution allows you to installed on upto 100 devices (including the ones you use for development), all you have to do is have the paid for developer account (the standard $99 one).
Here's one explanation, but there are loads of articles around on the subject:
http://furbo.org/2008/08/06/beta-testing-on-iphone-20/
Update Summer 2013: The limit now seems to have been increased from 100 devices to 200 devices.