One of the best places that I've found for doing sponsored posts is Social Spark!
I love it for three reasons:
1. They are incredibly well organized and their site is easy to navigate and see exactly what is going on! I get emails every time there are new opportunities and daily reminders too!
2. They pay on time! I can check my list of opportunities at any time and see exactly when they are going to be added to my balance and as soon as I decide to cash out I have to wait just a minute or two for the paypal transfer to go through and my money is ready to go!
3. Their posts are easy to write - you write them right on their site and all of the links, photos and graphics are there to drag and drop into your draft! You submit it on their site for review and if you need to make a change it happens before you post, not a week after ... like some of the offers out there! Changes are usually minor too, just adding a couple of words or changing the order of something - it's some of the easiest money I make on my blog!
I just cashed out $150 for Christmas Shopping and to pay for some blog promotion I'm doing - you can cash out after just $50 without a penalty, or like me, you can save it for when you really need it and transfer a larger amount - it's all up to you!
I also love (yep a 4th reason) that Social Spark works with larger name and reputable companies - ones I know that my readers will be interested in hearing and reading about, rather than some of the other sponsored post companies I've signed up for.
If you're looking for a way to make some extra money on your blog with sponsored posts, I highly recommend checking out Social Spark!