This seems almost too obvious to me, but there should be an easy way to generate an invoice for a customer based on the Products and Services that are added to their Tickets. Bonus points if this feature can let you checkbox which products and services to put on a given invoice.

Example: Customer walks in with computer problem, ticket is generated, diagnostic fee added to ticket and invoice created. Customer pays up front diag fee. Technician finds bad hard drive, adds new hard drive cost to ticket, additional labor, then selects just these 2 additional entries for export to new invoice.