I really don't know if any of my author profiles have done anything to help sell my Kindle books. I certainly have not sold any of the hard copies of my books, so my assumption is that it's almost all Amazon and Kindle that have successfully marketed my books, rather than the half-dozen author profiles. I gave up on posting on Twitter or Facebook groups almost immediately because my time was better spent creating lessons or working on websites rather than incessant promotion, though I can see the value if you have just one book you're trying to promote. However, whether you have one book or 100, you can at least appear to be a professional author by signing up for free accounts with some of the pages listed here. I am sure there are others, and you can comment below to ask me to add to the list.
Keep in mind that these are my profiles listed. Not all of them are perfect or complete, and I have only edited a few of the Amazon ones (since they are automatically generated). I think you need to have at least one Kindle or for-sale-on-Amazon title to list with them, but the rest of these are free. Some require your book ID to list, so that means if you printed it in your basement, you might not have an ASIN or ISBN, so go ahead and get one.
Websites or Blogs
Remember that you should have Twitter, Facebook, and Linkedin profiles, too. Many authors will have a Facebook author page in addition to one for friends. I have a main author page at McNewsy.com. However, I do more to promote myself on my blog at Satisfamily.com. In fact, when I write a story like this one, I might republish a version of it on a dozen websites, and there's nothing wrong with a free blog. When you check out my Amazon author profile, you'll see the blog showing up there.
Amazon Profiles (ones I have updated)
I dropped the ball on Canada and Australia so far, since I sell there, too. I will get those pages up soon. UPDATE - Amazon does not have profile pages in Canada or Australia yet.
Library Thing Profile
This seems to be the most popular of the sites besides Amazon.
Market List Profile
Marke List lets you post ads for your books that seem to get a lot of hits but no sales.
I know that's not the entire list, but it's a start if you are looking to promote yourself as an author. Once you get signed and have that big movie deal, then someone else will write the profile for you.