Many have criticized pornography as exploitative; there is plenty of anecdotal evidence that some workers are not treated with respect or dignity, particularly by certain producers.
More recently, though, there has been a move towards increased labour rights and respect of performers. The top performers have always made a good living and are typically treated well. The ethical pornography movement takes it one step further. A core part of the approach is that performer rights are paramount.
There is also concern that pornography negatively affects consumers. Porn likely affects different people differently, and type of content interacts with intrapersonal characteristics. The research shows that the consumers who we should be most concerned about are those (men) who are characterized by hostile masculinity (e.g., attitudes supporting violence against women, rape myth acceptance, hostility towards women, etc.) and antisocial traits (e.g., impulsiveness, low empathy, etc.). They're the same viewers who are likely to choose content that represents the worst of the porn industry (e.g., exploitative, misogynistic, etc.). For these men, porn use can increase risk for sexual violence, and also feeds their nasty attitudes about women.
Another concern is that porn is replacing sex ed for teens. Sex ed in some geographical regions is great; in most others, it's still pretty terrible or superficial. If teens watch porn without sex ed to balance it out, their blueprints for sex and relationships will end up being based on the fantasy world of pornography, and not reality.
As far as we can tell, though, the vast majority of porn consumers reject the type of content that could be considered problematic, and now that porn has become ubiquitous, many have argued that the industry is moving in a more positive direction (not all agree, however). There's also lots of new research coming out showing that porn consumption is related to all sorts of positive outcomes and experiences, despite the narratives you hear in the media and online.
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)
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.