Easy PayPal Custom Fields
This plugin makes adding a PayPal button to your site or blog very easy. There is no complicated shortcut syntax to remember (or to teach a client).
You can select on which type of post (including custom post types) you’d like to display the button.
There is a settings page for default values (username, currency etc), which can be customized for individual posts. (This might come in for sites with multiple users).
Choose from four custom button themes (with custom button text): light, dark, blue and red. If you prefer, you can simply display a standard large or small PayPal button.
Your PayPal username is converted to HTML entities so it can’t (easily) be harvested for spam by species 8472, or any passing Sith lord. It’s not a foolproof method, but it helps.
This plugin is created for WordPress 3.x and supports ‘Buy Now’ and ‘Donation’ functionality.