Based on the W3C's Web Notifications specification, here's a very useful service called Push.js which lets websites send timely messages to site visitors, whether on desktop or mobile. For example, let your visitors know when you add a new product or blog post, or use it to announce important, breaking news.
Intention.js is an alternative to using media queries to restructure your content. Using data-style attributes and classes you switch the order of your DOM elements to suit the device.
Designing (and converting) for multiple mobile densities - converting graphics for different resolution densities.
Just picked up Smashing Magazine's The Mobile Book. You probably should too.