If you are part of ebay partner network then WP TagAds is the best bet for you. This plugin allows you to easily add EBay listings on your blog and you can put them in the sidebar with the available widget you see on the blog.
With WP TagAds you are served eBay products based the keywords you assign to a post. Don’t like the ads your are seeing, just change the keywords around a little to get the ads you are looking for.
This is one of the best plugin when it comes to Ebay listing on WordPress blogs and I highly recommend it. It’s pretty easy to install the plugin and by following these instruction you can start displaying the ebay listings :
1. Download Package
2. Unzip contents to your plugins directory
3. Activate Plugin
4. Once you have activated the plugin, click on the WP TagAds link in the header and enter your eBay Campaign ID
5. Finally go to Design->Widgets and drag the WP TagAds widget into your sidebar.
6. All done!