I spent two days messing around with three tools last week to manage single/once off transaction customers for my hobby photography business. Then I remembered I bought the agency deal with Trafft. I am one of those sumolings who buys deals and can forget what I have. Just configured Trafft into a booking/sales landing page, i can deal with queries, generates invoices and also functions as a Client Portal. For my business it is a perfect CRM with Bells and Whistles perfect for the smaller business.

Highly recommended, as well as their Wordpress Sister Product.