One of the most underutilized FREE services offered to eBay store owners are eBays WONDERFUL promotion boxes.  Promotion boxes are a great way to cross sell within your store as they present additional eBay items to your customers wheile they shop various categories.  As most eBay sellers are very much in time-sensitive mode, you can set your store promotion boxed to automoatically disply items from your store based on a wide range of settings. 

To configure your promotion boxes, go to My eBay, then Manage my Store. The link to Promotion Boxes in on the left under Store Design!