WP-Invoice has been around for a number of years in numerous iterations but has consistently become better and better and today it’s completely rewritten.

WP-Invoice lets WordPress blog owners send itemized invoices to their clients. Ideal for web developers, SEO consultants, general contractors, or anyone with a WordPress blog and clients to bill. The plugin ties into WP’s user management database to keep track of your clients and their information.

Here is a list of some of the features offered by WP-Invoice:

Automatically import invoices from Web Invoice plugin.
WP-CRM Integration
Brand new user interface for much improved invoicing filtering and searching
Minimum and Split / Partial Payments
Invoices can be reassigned to a different recipient
Receipt Page with Invoice Log
Per-defined Line Items
Discount Line Items
Custom Payment Entry, and administrative adjustments
Customizable Invoice and Receipt Templates
Create invoices from the WordPress control panel
Prefill customer information using the WordPress user list
Send invoice notifications to customers with a secured link back to the web-invoice
Accept credit card payment via Authorize.net or MerchantPlus NaviGate
PayPal available if you don’t have a credit card processing account
Setup recurring billing using Authorize.net’s ARB (Automatic Recurring Billing) feature
Force web-invoice pages to be viewed in SSL mode
Archive old invoices
Easily use old invoices as templates for new ones
Dynamic and intuitive user interface
Custom tax label, states input, and PayPal button URL
Insert an “Invoice Lookup” form using PHP or WordPress Shortcode anywhere
Create users directly from WP-Invoice
Customize billing settings per invoice
Customize invoice notification email per invoice
Invoice notification, reminder and receipt templates
Export/Import Invoices [Power Tools]
Sales Visualization [Power Tools]

Download: WP-Invoice