It seems like only yesterday that real estate investment trusts (REITs) were viewed as the next shoe to drop during the global credit crisis. Back then, plenty of REITs cut or suspended dividends while a couple even filed for bankruptcy. Those days are long gone as one of favored asset classes among income investor have come roaring back over the past couple of years.

As a group, REITs rallied so hard and so fast in 2010, that many analysts and so-called experts were left saying the asset class was overvalued. That may have been the case and there probably are more than a few REITs that are overvalued today, but the assertion that REITs are too pricey glosses over a crucial fact: They are high-yielding instruments and in a yield-starved environment, investors may be willing to ignore valuations in an effort to generate income.

Along those lines, it's not surprising that a plethora of REITs are outpacing the S&P 500 by handsome margins this year. Let's have a look at a few here.

Pennsylvania Real Estate Trust (NYSE: PEI):

Pennsylvania Real Estate Trust manages, develops, acquires, and leases mall and power and strip centers in the Eastern U.S. With a yield of 4.1%, the company expects funds from operations of $1.83 to $1.90 per share this year, inline with mean estimate of $1.90 per share. The FFO number is important because Pennsylvania Real Estate Trust's current payout is less than a third of what was before the financial crisis. The 40.5% year-to-date returns could grow with an increased dividend.

Macerich (NYSE: MAC):

California-based Macerich is a shopping center REIT and that gives the company exposure to the health of the U.S. consumer. In fact, the shares have proven to be a useful way of gauging how the consumer is feeling. For a REIT, Macerich's 3.7% yield is pretty ho-hum and yes, Macerich cut its dividend during the financial crisis. That said, the distribution rose by 10% last year and the REIT has offered year-to-date returns that are better than double those offered by the S&P 500's.

American Capital Mortgage Investment (NASDAQ: MTGE):

American Capital Mortgage Investment is a mortgage REIT that was started by some executives that used to be part of American Capital Agency (NASDAQ: AGNC). With a market-cap of less than $225 million, American Capital Mortgage is a micro-cap stock, but nothing else about this stock is "micro." Certainly, not the 21.6% year-to-date return, nor the whopping 16.4% yield.

Dynex Capital (NYSE: DX):

Dynex Capital is another mortgage REIT and it's fair to say to its 5.2% year-to-date return isn't too impressive. Over the past five years, Dynex shares have outperformed the S&P 500 index by about 100% on a normalized basis and the dividend has risen by more than 50% since 2009, according to Brad Prigmore. The current yield is 12%.