Hundreds of spectators gathered around the Manhattan federal court where Bernard Madoff -- the perpetrator of what is believed to be the biggest Ponzi scheme in history, responsible for bilking thousands of investors of billions of dollars -- was sentenced to 150 years in prison on Monday. While Madoff may be claiming most of the headlines, there are plenty of other Ponzi schemers who have been more or less flying under the radar.

In fact, the Securities and Exchange Commission has filed 32 complaints alleging Ponzi or Ponzi-like schemes so far this year, a "significant increase" from last year, according to Scott Friestad, the associate director of the SEC s Division of Enforcement.

In most Ponzi schemes, investors are offered too-good-to-be true returns when, in fact, the perpetrator is just using the new investors' money to pay off the old investors, giving the impression that the business is legitimate. But these days even crooks are suffering from the recession.

See 5 other alleged Ponzi schemers

Ponzi schemes, to succeed, are dependent on having positive cash flows, and the current economic crisis has dried up their funding sources, so many of them have collapsed, says Friestad, who says the SEC has recently stepped up efforts to pursue such cases.

The SEC has its work cut out for it. The Internet has enabled Ponzi schemers to easily reach out to hundreds or even thousands of potential victims, says Friestad. William Wise and Kristi Hoegel, for example, allegedly stole $68 million from investors, many of whom they solicited online, according to a complaint filed by the SEC.

Some schemes are more home-grown, using an element of what s called affinity fraud, or fraud that targets victims with a similar religious, ethnic or cultural background, says Jacob Zamansky, a New York lawyer who specializes in securities law and represented some of the investors in the Madoff case. Recently-accused schemer, Clelia Flores, targeted her Hispanic-American community in California, using word-of-mouth recommendations and other tactics to find new investors, according to the SEC.

Just because somebody is from the same religious or ethnic background as you, that s not a reason to drop your guard, says Zamansky. Ponzi schemers and other fraudsters often use that kind of connection to establish credibility, he says.

Of course, the most common thread these schemes share is the promise of returns far beyond anything legitimate investment opportunities could ever offer. We regret every day that we didn t catch it sooner, Friestad says of the Madoff scam. But investors themselves are the first line of defense. One of the positive things to come out of the Madoff indictment he says, is that investors may be more suspicious of returns that sound too good to be true.

Madoff investors aren't the only ones learning a hard lesson. Here are five alleged Ponzi schemes that are currently under investigation, in order from smallest to largest amount of money stolen.

Amount allegedly stolen: $23 million

: The SEC alleges that Flores targeted the Hispanic-American community in the Los Angeles area, promising returns of up to 25% in just 30 or 45 days to those who made investments with her company Maximum Return Investments.

The scheme

What the money was allegedly used for: According to the SEC, Flores took more than $3.5 million for personal use, using over $400,000 to buy a house. She also allegedly threw a lavish company party to celebrate her company's supposed success.

Status: Flores failed to file an answer to the SEC s complaint by the June 12 deadline, so the SEC will file a motion for a default judgment. Flores s lawyer, Wayne Little, says she is working with the SEC to resolve the matter. I m assisting her in putting together the documents to figure out what s owed and what s outstanding and what happened, so that the right thing can be done, he says.

Amount allegedly stolen: Between $50 and $75 million

: The self-proclaimed Chinese Warren Buffett, Tang allegedly targeted victims in the Chinese-American community for investments in his Toronto-based hedge fund, Oversea Chinese Fund Limited Partnership. According to the SEC complaint, Tang admitted the fraud to investors in February and asked for more money to help him recoup their losses.

The scheme

What the money was allegedly used for: $9.6 million in investor funds is unaccounted for, according to the SEC complaint.

Status: The SEC obtained a temporary restraining order and a freeze on Tang s assets in April. The next step is a hearing on July 23 on a motion for a preliminary injunction that would prevent Tang from trading in the future. Tang also faces securities fraud charges in Canada, according to the SEC.

Calls to Tang s Toronto-based lawyer, Loftus Cuddy, were not returned by press time.

Amount allegedly stolen: $200 million

: Guidi, Armitage and Koenig allegedly recruited elderly California investors for real estate projects, including a number of assisted-living facilities in several states. The California state attorney general alleges that when the businesses lost money, new funds were used to pay off old investors instead of being invested in the facilities.

The scheme

What the money was allegedly used for: Guidi, Armitage and Koenig spent investor funds on expensive wines, art, luxury vehicles, lavish vacations, an 80-acre castle estate and a Lear jet, according to the California attorney general.

Status: Defense lawyers have won a delay of a preliminary hearing, pleading that they have over a quarter million pages of documents to sort through, according to the attorney general s office. They ll be back in court July 29, at which time the date for a preliminary hearing could be set, says the deputy attorney general. James Koenig s lawyer, Deputy Public Defender Michael Horan, confirmed this account of the status of the case. The men face charges of securities fraud and burglary, because the alleged fraud sometimes took place in investors homes, according to the deputy attorney general. Under California law, anyone who enters a person s home and commits a felony can be charged with burglary. Jeffrey Guidi s lawyer, Ted Cassman, did not return calls by press time.

Amount allegedly stolen: $370 million

: Cosmo allegedly recruited investors for a company called Agape World, Inc., which supposedly provided short-term loans to businesses, promising interest returns of 48% to 80% a year.

The scheme

What the money was allegedly used for: According to the New York State attorney general s office, less than $10 million of the $370 million raised was actually used to make legitimate loans.

Status: Cosmo pleaded not guilty. A bail hearing scheduled for last week was cancelled, and no new date has been set. Cosmo remains in custody. According to Cosmo s defense attorney, Stacey Richman of the Law Offices of Murray Richman, all conditions for his release on bail have been approved, and they re just waiting until a second phone line can be installed to allow for Cosmo s calls to be monitored.

Amount allegedly stolen: $8 billion

: Stanford allegedly sold fake CDs in the Antiguan-based Stanford International Bank, promising interest rates of as high as 7.8%, according to the SEC complaint. The SEC also alleges that Stanford and associates falsely told investors that the bank had no exposure to losses from Bernard Madoff s Ponzi scheme. According to the SEC, the bank was operated by Stanford s close family and friends, including Stanford s father and his college roommate.

The scheme

What the money was used for: Significant portions of the bank s portfolio allegedly went to undocumented personal loans to Stanford, and real estate purchases, according to the SEC complaint.

Status: Stanford faces both civil and criminal charges. Typically, a civil case will be stayed while a criminal trial proceeds. Stanford pleaded not guilty to the criminal charges at a detention hearing last week, and his defense team is asking for a year to prepare for trial. Another hearing in the next few days will set a schedule for the case going forward. Calls to Stanford's lawyer, Dick DeGuerin of the firm of DeGuerin & Dickson in Houston, were not returned by press time.