I added the Giveaway Scout button to the very bottom of my blog. It shows readers all sorts of giveaways that are going on in the blog world. Giveaway Scout is a giveaway search engine. Users subscribe to receive updates on the latest giveaways on the web. You can add your blog and your giveaways will be exposed to a large network or users.
They publish your giveaways on multiple channels (Their web, newsletter, Twitter, Facebook and widget network) and it is 100% Free of charge.
Check it out here!