The WatchCount.com WP Plugin is a free eBay WP plugin that shows Most Popular (or a seller's) eBay items in a blog's sidebar or posts.
I'm going to give this 4 stars out of the box. I've only had it installed for 2 days and wrote to the developers for support and was contacted back within 24 hours.
Coming from a design background I would like the widget to be more customizable. For instance the font size of the product title.
The developer did however send me an example of a website that managed to customize the size so I think if I just give it another 15 or 30 min (looking at this sites code) I'll be able to achieve my desired look.
Two days in, I'd say go ahead and install this plugin if you need your ebay feed in widget!!