Simple Business Invoicing and Inventory
Easy to use software for estimating, invoicing, inventory, billing and customer management. New version supports credit card processing.
http://www.owlsoftware.com/sbi.htm

GST / VAT Accounting and Invoicing
Easy to use accounting, invoicing and inventory management software with special tracking of Value Added Tax (VAT) or Goods and Services Tax (GST) collections and payments.
http://www.owlsoftware.com/gstvat.htm

PetroXML
A DTD for vendor invoicing for oil and gas field operations.
http://www.petroxml.com

Survivor Software
Survivor Software publishes MacMoney and InvoicIt, the best money management software available for a Macintosh.
http://www.survivorsoftware.com/

Invoice It!
Inventory, billing & invoicing Software designed for businesses with tiny budgets, but big demands, invoiceit! the complete business tool.
http://www.scrambled-card.com/

Tenant Mail
Automated Invoicing for the Apartment Industry. Every invoice includes a return envelope, stamp, and perforated payment stub. Custom messages or notes can be added on the monthly invoices. Additionally gives companies the ability to send custom letters and announcements.
http://www.tenantmail.com/

CPqD
Offers OSS system that handles rating, invoicing and collections.
http://www.cpqdusa.com/

The Invoice Store
Video store rental software and invoice software products. Awarded 5-Star ratings and editors choice for best software. Download a free trial version. Scanners, cash drawers, receipt printers and pole displays available at discount prices.
http://www.softstore.net/

Factor Systems
Billtrust provides innovative paper and online billing services that save you time and money by using a strategic approach to billing outsourcing.
http://www.factorsystems.com/

Bowen and Groves
ERP Software from Bowen & Groves - M1 by B&G the affordable, user friendly system for small to medium manufacturers
http://www.bowen-groves.com