I want to echo the other comments here that low expense ratio (<0.25%) funds from Vanguard, Fidelity, Schwab, etc... are all great stable investments.
My time horizon is longer than 5 years, and I buy broad market index funds split up as follows: 55% US large cap (e.g. VIIIX, VTSAX, SWTSX), 15% US mid cap (e.g. VMCPX), 10% US small cap (e.g. VSCPX), and 20% international (e.g. VTSNX, SWISX, VXUS).
I also highly recommend dollar cost averaging. i.e. buying a fixed amount of your portfolio at fixed periods. I have my bank do this automatically every 2 weeks. The benefit of dollar cost averaging is (1) it takes the emotion out of investing, and (2) over a long time window, more of your assets will be purchased at a low prices than high prices (because you're buying a fixed dollar amount of assets every N days, fewer you will buy fewer assets when prices are high and more assets when prices are low).
My time horizon is longer than 5 years, and I buy broad market index funds split up as follows: 55% US large cap (e.g. VIIIX, VTSAX, SWTSX), 15% US mid cap (e.g. VMCPX), 10% US small cap (e.g. VSCPX), and 20% international (e.g. VTSNX, SWISX, VXUS).
I also highly recommend dollar cost averaging. i.e. buying a fixed amount of your portfolio at fixed periods. I have my bank do this automatically every 2 weeks. The benefit of dollar cost averaging is (1) it takes the emotion out of investing, and (2) over a long time window, more of your assets will be purchased at a low prices than high prices (because you're buying a fixed dollar amount of assets every N days, fewer you will buy fewer assets when prices are high and more assets when prices are low).