Blog giveaways are only a good thing for you if you have a website or etsy store and if the blogger writes a detailed write up with pictures of the product in use that you sent. Here is an example of a good product review that I had done recently: http://alli-n-son.com/2010/06/08/
Good bloggers get paid in the form of your item that you send. As another poster mentioned, a good blog review takes time to research, write good content, take good pictures and link back to your site and product(s). Also they should put your button up on their sidebar if you have one. There are many crappy bloggers out there that are just looking for free stuff, so be wary.
In my opinion, a good blog has lots (hundreds or thousands) of followers/readers/commenters and has a page rank of at least 3. Also you should ask how many visitors they receive in a day to their blog. Asking for references is a good idea too.
Also many other WAHM (work at home moms) will do product reviews for free and you don't need to send a product. I am going to be offering that service soon and here is a couple of good websites to get a free review from: http://nannydeprivedreviews.blogspot.com/ http://www.5minutesformom.com/mom-owned-stores/join/
There are many others, but this will get you started for now. Hope this helps.