You can always purchase an item you think your readers would like to giveaway as well.
If a company contacts you about doing a blog post about their company, ask them to sponsor a giveaway! It will give their post more views!
Another great idea is to have an entry (on the Rafflecopter) for when participants share the giveaway on their Facebook, blog, Twitter, etc. This gives your giveaway more exposure, in turn giving your blog more exposure.
What are your giveaway tips?