Bonds are the easiest vehicles to correlate risk vs. return without taking a position. The coupon values are stated clearly, and there are several agencies that can inform about credit risk. If you wish to purchase the actual bond itself, you have the stats on the company, cash on hand, NAV, and so on. If you want higher return, buy from companies with riskier stats/credit (junk). One strat is to buy emerging market junk bond funds, to distribute risk of default.Are there any forms of investing that are considered higher risk, but expected value/ROI goes up to compensate? I remember wishing I had 20k to dump into BoA when it was at 6$, because it seemed like the odds heavily favored buying some stock and if I did end up losing my 20k it wasn't a bid deal. With 25-30 years until retirement, it seems like there might be good places to make money that carry higher risk than an older person would be willing to live with. However, I have no clue what those opportunities might be.
You can also increase leverage to increase return (and risk) for many investments such as stocks, real estate, options, futures and so on. However, much of this is pure speculation. Unless you have inside knowledge of whats going on, you have a 50% chance of making/losing money.