There's an entire page of eBay's quarterly power-seller newsletters dedicated to time-saving tips and tricks. Previously, the availability of high-quality eBay listing tools is a bit limited for macs.

Thus GarageSale, the OS X shareware lister that is one of the best out there on any platform (and one that supports eBay Motors, too). Perhaps coolest of all, GarageSale supports iPhoto, so doing multi-photo listings is a snap. If you sell complex items on repetetive basis, this application can be a huge time saver.