I was in need of a Quickbooks and Nopcommerce integration for my store, I decided to give JMAwebstore a try      http://www.jmawebtechstore.com.  The software is great and the developer worked with me on some of my needs for integration with my store.  The service from JMA was excellent.  I highly recommend this company for the Quickbooks Plugin, I have not tried any other plugins yet of theirs, but I am sure the other plugins are great too.  The Quickbooks plugin they have is by far the best that I have used, and makes it so much easier to manage my nopcommerce site.