Perhaps the most audacious of the firms known for massive penny-stock scams was Robert E. Brennan's First Jersey Securities, the subject of my current research. Unfortunately, what little I have written on the subject in academic journals is not available without subscription and thus can't be posted here. I could link to numerous internet pieces re: Brennan or FJS, but choosing which of the thousands of sites discussing the inter-related topics is a challenge. A quick primer can be found here in Forbes magazine, which dogged Brennan throughout his fabulous rise (and contributed to his precipitous fall).
As for Brennan, he resides in the Federal Correctional Facility (FCI) in Fort Dix, New Jersey, where he is serving time for bankruptcy fraud. According to the Federal Bureau of Prisons web site, he is slated for release in December 2011.
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One last note: Some useful resources for anyone researching or investigating stock frauds will soon be found on a page I am creating. These will be a blend of government and private agency sites, along with several academic and quasi-academic sites. Hopefully, when completed the page will become a tool for students and academics, and also for the general public. In advance of that comprehensive page, these may be of assistance:
U.S. Securities and Exchange Commission (SEC)
SEC Penny Stock Rules
SEC Microcap Stock Guide for Investors
North American Securities Administrators Association (NASAA)
Financial Industry Regulatory Authority (FINRA)
FBI White-Collar Crime and Fraud