A contact form can serve as a simple order form for your products or services. Contact Form 7 together with a few other WordPress plugins can be used to create just such an order form.
contact form 7
Captcha-less Hashcash spam protection for Contact Form 7
Contact Form 7 is the most popular contact form plugin for WordPress. WP Hashcash is a javascript based captcha-less spam protection plugin for WordPress. Hashcash for Contact Form 7 is a plugin that I have coded that bridges WP Hashcash and Contact Form 7 allowing you to protect your contact form with a captcha-less spam prevention system.