Password Sentry - Fantastic software for locking down a site based on passwords.  Uses geolocation to make sure that passwords are not being shared, a much better alternative than cookies, or IP addresses. If you want to make sure your site is locked, this the software to use.  Integrates with SiteLok (above), WordPress, Joomla,

CB Protect - If you just want to protect an eBook this may do the trick for you. Integrated perfectly with ClickBank. (around $30/month).

Active E-book Compiler - A one time fee for a decent protection mechanism. Unfortunately this one only runs on PC's and Microsoft Windows operating system ($49.95).

DPD - Protect your digital products for a single flat rate every month. Setup/manage affiliates too, all at no additional charge.

DigiVendorPRO- An excellent choice for selling a digital product, if you only require PayPal as your payment option. Let's you easily hide your product securely outside of your website.

WP PDF Stamper plugin - An alternative to PDF file locking. This WordPress plugin will stamp the contents of your PDF files with the purchasers name, email, address, etc.  Integrates with ClickBank, nice.

DLGuard - An excellent choice for membership software management and digital product downloads. Supports all major payment processors.

CBProtect- The best way to protect Click Bank content: PDF files, or anything else. The file will be locked specifically to your users computer, so it cannot be copied. Compare it to other mechanisms as it does not require a monthly payment to continue using it. You only pay for the files/downloads that you protect, so if your volume is minimal this is a good choice.

OpenCrypt -A legacy script that can protection applications, now expanded to include memberships, blogs, and other features.

Locked Area - This older version of OpenCrypt gives you an excellent idea of what it is capable of. Lite version is free. Written in Perl and not PHP.

Directory Pass - an excellent, free open-source htaccess file handler and protector.

HASP-SRM - Looking for a hardware key? Aladdin will give you software locking features that are hardware driven. I've used their hardware keys for protecting my own software for many years.

Simple Member - A basic Membership script. It is older and may be lacking some features available in the newer softwares.

The Membership Script - This new one says it can 'do everything'. Unfortunately it is expensive.

E-Power-Wrap - Ebook software/wrapper that will let you compile your PDF files into an executable .exe file and distribute it with licensing rights required.  A lower cost protection mechanism.

Desktop Author - EBook electronic publishing software.  Full support for digital rights management (DRM), and the ability to lock content of all types (including multimedia content).  Redistribution is allowed and payment processing handled completely by their store at Ebooks.com.

XSitePro WordPress Blog Protection & Security

Zaxaa Member - A free WordPress blog protection plugin that integrates with the Zaxaa selling platform. I am using this myself. It provides a full affiliate program, shopping cart, storefront, and everything else you would need to start selling online.  This truly stands up to it's tagline: The World's EASIEST & FASTEST Online Selling Solution.  Download your Free Zaxaa Membership Site WordPress Plugin here . Find a video Tutorial on setting up and using Zaxaa Member here.

WishList Member - Membership software for WordPress. A community is also available for helping you increase signup and retention rates and with specific plugins.  One of the better options for locking down a WordPress Blog (but you should also look at DAP-Digital Access Pass, below).

DAP (Digital Access Pass) - One of my favorites for membership protection software and digital download protection. You can run DAP inside of your WordPress Blog, or on a standard website. Includes a autoresponder as well as an affiliate system. Full supports online stores, forum integration and more.

Easy Quick Member - Fast membership site creation from the Profits Theme company (Get Profits Fast).  They have built an amazingly easy and quick membership builder that supports drip memberships, Amazon S3 file protection, Goto webinar integration, auto list building, magic content, sneak-peek content, retention reports and more.

MemberMouse - A great WordPress Membership plugin with features not found elsewhere: built in affiliate integration with iDevAffiliate, customer management and built-in support automation.  Reasonably priced, but it does require a monthly payment. Excellent documentation such as this list of Extensions, Knowledgebase, and User Community. Integration with BBPress (the forums used by WordPress) and support of Braintree (similar to Stripe) as a payment processor, signup for Braintree here. Note that some features require a card-on-file payment processor, as indicated by this recurring billing information: With card-on-file payment services, the MemberMouse plugin on your site is responsible for keeping track of the payment schedule and sending payment requests to the payment service (i.e. Stripe, Braintree, Authorize.net CIM). As indicated on this Recurring Billing page.

SiteManPro - A upcoming WordPress protection/membership software system that has a lot to offer. Feature set is worth looking into, and comparing with DAP (above).

SUMA Plugin - Subscription management for WordPress. A plugin that allows for secure merchant account payment processing as well as PayPal inside your WordPress blog.

XSitePro Amazon S3 File Protection & Security

TutsPlus - Amazon S3 - Excellent tutorial on using Amazon S3 to store/manage files with ease. Backup your server, or local computer.

S3 Flowshield - The number one product for protecting streaming content inside of your Amazon S3 account.

Amazon S3 Security Webinar - A full webinar that describes how to protect your content inside of Amazon S3, from the author of Amazon S3 Flowshield (see above).

CDN Vault - Protect your content in WordPress or Joomla websites using this excellent plugin. Comparable to S3 Flowshield but does not offer protection to content outside of WordPress/Joomla.

Amazon S3 PHP Class - If you're looking to 'roll your own protection' this is the way to go. A well documented PHP class written by Donovan Schonknecht. You can drop in and use it anywhere.  Find full documentation, and a huge page of comments on how to use it.