I invest in a range of small-cap funds (Canadian and American), ethical funds, and mutual funds. The return on these is medium-high but they are also sensitive to market fluctuations. Since I'm not anywhere close to retirement, I'm not worried about it because statistically, the funds will increase with time. I also invest in Canadian bonds for their guaranteed return and use them as a way of saving for a big-ticket item (i.e. down payment on a house).
I invest through Investors Group (I don't know if they are in the US as well). I pay a fee for their service but I don't have to keep as close an eye on my investments. I meet with my advisor quarterly and discuss how the funds are doing and if any changes need to be made. I consider the service to be well worth the payment since it leaves me with time to deal with everything else going on in my life.