Hi T.,
A 529 plan is a great way to save for college expenses, but it does require some research. Where you put the money depends on the amount. As mutual fund companies go, I like Vanguard, because they are a no load fund, but you have to have a good sized deposit to open accounts. You can go to vanguard.com to research funds, they even have a computerized planner that will help you to decide what types of funds, or mixes of funds would suit your risk-tolerance the best.
Know that if you go with a mutual fund, you are investing in the stock market, or bond markets, or money markets, and all are subject to growth and contraction. It is best to invest spread the money around a little into different types of funds, so you have some in growth, some in balanced (stocks and bonds), and in international (all countries, not just USA), etc. When you "invest" the money, you want to invest it for at least 5 years. This is a particularly good time to invest in the markets, too, as prices are still lower than usual, and are beginning to climb out of the trough.
If the ups and downs of the market are scary to you, and you will cringe with anxiety every time the market contracts, then go with a bank plan. You'll earn less (or your son will), but you won't be worrying about the money.
Whatever you eventually do, be sure you understand what you are doing and how the funds work. You can do a lot of research online, but if you have questions, I know at Vanguard, you can call an 800 # and they people on the other end (people, amazing !) are very helpful.
This is a fantastic gift someone has given your son ! It will be a wonderful thing for you later, too, when he needs the money for school. I think the hardest thing about receiving the money at this particular time, however, is that there's no way you can go back and say, "thank-you." So, do your best with the money, make good choices, use more than one fund (if there's enough $$ to do that) to spread the risk around a little, and live your life with thankfulness of spirit knowing that you and your son were loved enough by this person that they started the educational funding for you ! It's wonderful !! :-)