Real Estate Investment Trusts (REITs) are great for income and asset-class diversification. Starting with the latter, this is a great way for investors to get exposure to real estate without having to jump through the operating hoops best left to those who pursue the field as a profession, and without having to treat their homes as if they were pork-belly futures. (Click here for an example of a well-reasoned discussion of the merits of REITs relative to investment via private equity funds.)
As to income, REIT yields tend to be well above those of corporate