Investing in coins and collectibles: Buffalo nickels and Spiderman comic books are good examples of coins and collectibles that can rise in value, and thus offer opportunity for passive income investors. You'll need to get up to speed on the value of any coin or collectible under consideration, but once you do so, you're on the way to price appreciation on a commodity you'll be paying a lower price to buy, and will garner a higher price when you sell.

The U.S. Internal Revenue Service categorizes income into three broad types, active income, passive income, and portfolio income.[1] It defines passive income as only coming from two sources: rental activity or "trade or business activities in which you do not materially participate."[2][3] Other financial and government institutions also recognize it as an income obtained as a result of capital growth or in relation to negative gearing. Passive income is usually taxable.

I’ve never invested in real estate (except to live in), but am always intrigued by communities like FS who seem to have such a passion for it. My intrigue stems back to my earlier comments that the long term trends in appreciation in real estate are simply not very competitive versus equities, despite what Robert Kiyosaki had to say in his book, Rich Dad, Poor Dad.
My dad is in  a similar situation as we speak, things have not been going well for him at work (but I do think he has himself to blame) and seems likely he will get let go.  Mr. Budgets and I both see how our parents are and we totally want to be on the other end of the spectrum when it comes to how they handle money. It motivates us to save and invest even more.
Portfolio income can come from multiple sources – interest/bond coupons, stock dividends, financial strategies including derivatives and capital growth.  Each offers some cash flow and some also offer potential capital gain with some risk from liquidity and volatile prices.  In this low-yield environment, many investors rely too heavily on cash flows and to pursue this are venturing further into riskier areas than they’d normally consider.