Apple's Airport Express is very portable, but should be setup with some security parameters using an actual computer before use. Apple has an application to do this, but it cannot be done from the iPad itself. Once set up, though, access through an iPad should be fine.
Most other wireless access points have a web-based setup, which can be accessed from the iPad through a browser (Safari, or any other browser you may have installed). D-Link makes a portable one: DWL-G730AP that might work for you. I have not used it, but it seems to get good reviews.