Here is the link to the one we have been looking at. Definitely something we plan to have before our first show this next fall!
https://squareup.com/
When we went to the San Diego Super Show last year we sat and talked to Jeff Luman about it for awhile and he said he really like it. We used it and it was very simple, just stick the scanner in the jack, go to the app, swipe the card, enter the price and sign.
And you can also manually enter CC#'s with it! It cost alittle more 3.5% + $.15 per transaction instead of the 2.75% when swiping.