Prosper & LendingClubGreat to throw $20k at, but there's a bit of work to keep 'em performing. Great returns.
TreasuryDirectPoor returns, but online trading and ACH make even the 28 day T-bills easy and liquid.
Gold, Silver and other commoditiesFrom a coin shop, eBay, or now even as an ETF (Symbols SLV,GLD) for liquidity. 3% average performance for gold. Gold & silver have done well over the past few years. Other commodities have perked my interest of late.
ETFsGreat for real diversification. Often highly volatile, fully liquid. I like them because they offer positions that you cant get anywhere else. Where else could I short the entire US commercial real estate sector in aggregate? (Commercial Real Estate Ultra-Short I think)
LandUS & foreign (first world). Unfortunately it requires a bit of luck picking the right area, amenities, climate, soil, road access etc. Can't start for less than $35k. Highly illiquid and generally poor returns. I've been looking again lately.
Stocks & FundsStill not seeing consistent returns from long holds, only from buying and immediately setting 10-20% sell orders. What am I doing wrong here? Lately I've been hiding under index funds.
Venture FundsPeople keep bragging about them, but I still haven't seen good returns, even viewing all my experiences in aggregate. Roller coaster ride. Highly illiquid. Bad for blood pressure.
Your moms MortgageDon't laugh. Good returns. I know of 2 people collecting the line of credit rate minus 1%. Charity begins in the home. Keep the money in the family. Cliche, cliche.
Foreign CurrencyWouldn't recommend using a forex platform as the broker makes all of your money, not you. This is because you need to make the broker his spread before you can sell. Had success with xe.com.
RentalsAs long as you can do the math and factor in all the variables (i.e. future value of your deposit) they can work. Very illiquid. Potentially lots of work. Legal risks.
My own debtThis has actually been my best performing investment - myself. Zero anxiety. Freedom from the shackles of having to hold a regular pay check. High returns. (9% credit card quietly crept to 19% - what happened?)
Always interested in further diversification.
Mod: Changed "EFT" to "ETF" as they are very different terms in the finance world. - Foo