I've already discussed ethical and non-ethical porn on the blog previously so I'm going to pass it over to Violet Blue for her insight. If you have the stomach for it, contrast her recommendations with the content produced by people like Max Hardcore and Khan Tusion.
(VB's recommendations at the bottom)
She's an expert on everything sex - she's an educator, a writer, and sex-positive advocate superstar. I posted some of her work early last week. Her website (link here) is an excellent resource for all things related to sex, including ethical porn. She's written several books, including Best Women's Erotica 2010/2011/2012/2013, A Smart Girl's Guide to Porn, and Fetish Sex: A Complete Guide to Sexual Fetishes. There's a sample chapter from A Smart Girl's Guide to Porn posted on Oprah's website: link here.
Ms. Blue regularly posts softcore and hardcore galleries from some of her advertisers, who she's chosen because of their commitment to quality and ethics. The advertisers appear in the sidebar of her site. Keep in mind that her tastes are varied, and that she's into women and men. Here are some samples from her list of advertisers, past and present (click names to link to sites - very NSFW!!!!!):
Lust Cinema - the brainchild of feminist porn producer/director superstar Erika Lust; something for everyone (girl/boy/queer)
Dorcel Club - mostly hardcore, "luxurious" porn (boy/girl, girl/girl)
Girls out West - featuring "natural girls", softcore and hardcore (boy/girl, girl/girl). a similar site: Abby Winters
Explicite Art - original hardcore and softcore from France, diverse ethnic backgrounds (boy/girl, girl/girl)
Nubile Films - "capturing the essence of sensuality", (boy/girl, girl/girl)
For the Girls - featuring heterosexual content for women, softcore and hardcore (boy/girl), erotic fiction
Joymii - hi quality hardcore and softcore, "The Art of Erotica" (girl/girl, boy/girl)
Some other similar sites: Watch 4 BeautyErrotica ArchivesBright DesireJoy BearPink LableCocky BoysHot Movies for Her - online store featuring movies for women (or at least appealing to women), including user reviews
That should get you started on your research (for academic purposes only!). More sites are linked from Ms. Blue's website.
Sadly, few of her recommendations are intended for gay and lesbian consumers - perhaps you have some recommendations of your own? In the reply section, I've included a list of producers making "real" lesbian porn. It's by no means exhaustive.