I don't have actual "products" to offer up for giveaways (though, I'm currently giving away an apron ;P), but have a couple of ideas...
Ask the bloggers for site statistics. How many readers do they get per day/week/month. You won't want to offer up a $50 gift when the site only gets 4 visits a week.
Confirm up front how the giveaway will be handled... Will you pay to ship the product? If so, will you ship outside of the US? OR will you send the product to the blogger and let him/her handle shipping?
Can you offer a discount to those readers who want to try your product, but don't win? I see you have an MDC one, so that shouldn't be a problem for you. =)
Just a few ideas... hope that helps some!