I found this article while cruising through Reddit. It’s several months old, but the information is probably still really valuable.
Not all of the idols featured on this site are indie, and the indie scene is so big and diverse that it would be nuts to even try to encompass everything (even the forthcoming companion site won’t try that), but we do have a soft spot for those self-managed, in-it-for-the-love-of-performance idols who “tour” Tokyo or Osaka and have a handful of devoted wotas and otherwise sweet, delicious anonymity outside of the clubs.
This is also a good opportunity to link again to good friend Pure Idol Heart (site / Facebook), who seriously follows the indies and smaller agency talents. There’s another real insider look to the process of becoming and being an idol that you should look into.