A current campaign for Pizza Hut on a number of UK parenting blogs takes the theme 'free activities' and gets the bloggers to write about what they did over the summer with their kids for free, while mentioning the Pizza Hut Kids Go Free promotion.
The People's Republic of South Devon
Blogging with Dr P
I really like this because it's clearly listed in all cases as a sponsored post, so it's very open and above board, the bloggers have been given a genuine reason to write, the subject matter is relevant to the blogs, and it's also perfect for the target audience.
As far as I can work out this was done through eBuzzing, but if you know different let me know!