LeWando, Heather and Dan are great to follow about professional development. Specifically, Heather focuses on Gen Y professionals and Dan is an expert in personal branding. Jay and Brian are social media experts. Make sure you construct your PLN in a concentrated area. They all have blogs which are great reads and of course, you can follow them on Twitter. If you do, I suggest considering two separate lists so that your social media experts are on one list and your professional development experts are on another. I highly recommend Brian Solis' books - he is one of my favorite authors regarding social media. Jay has a great book as well. Robert Starks Jr.