Here’s a pretty cool concept for Moodle 2.1+, an enrollment plugin that let’s you invite students via email. Great for a no-non-sense ease of use enrollment. If the plugin works as described you can simply enter the emails and students are enrolled as soon as they click the link (assuming they follow through the registration process or are already registered on the site). It’d be a great addition to a paid courses site where students might pay via invoice.
I haven’t had a chance to test it yet, and it’s released only as a beta according to the developer, Jerome Mouneyrac, but it’s definitely one to watch.