Not sure how small are you looking for, but have you taken a look at Epicor? it has some great alternatives for small and medium businesses and its main products are based on .Net technologies and at least Vantage 8.03 and Epicor 9 offer great programming tools for customization. You can email me if you need more info about them :) if not you can just take a look at www.epicor.com

--PuLk