Is it better to put down 20% (if you can) or finance 100% of your purchase price, and invest that 20% somewhere else?

Apparently, it's better to put 20% down. You'll get a better rate on your 80% loan, if you don't take out a second, "piggyback" loan (or, if you get the same rate, your origination fees will probably be higher). In addition, you'll get a better mortgage loan rate on your 80%, plus your investment is guaranteed (more so than putting it into the stock market, at least).

Details: 100% financing : Why putting money down is a better investment choice - By Jack Guttentag, Inman News, by way of The Boston Globe