I currently only feel comfortable recommending the following agencies. 

World Modeling
A very professional agency and the longest standing adult talent management in Los Angeles.  I have worked with them & find the owner to be one of the most trustworthy in the business.

Spiegler Girls
One of the the most popular agencies with some of the most popular adult stars.

LA Direct Models
One of the top agencies as of current.

If you are an agent or agency who would like to be added to the list, feel free to drop an email, with your contact information, website & references.

XXXporntalk.com has an updated list of most of the adult agencies and managers here.