A lot of your decision depends on what you are saving for. If you are going for long-term savings with no definite plans for it (therefore you can afford some risk), stocks and mutual funds (index fund) are usually a good bet, although at $100/month the brokerage fees would be taking a pretty hefty chunk so you might want to save it in a money market account in the mean time and buy shares every 6-12 months.

If you have a goal for the money, like saving for a down payment on a house, then where you save it depends on your risk tolerance and time frame. Money market funds and CD accounts aren't glamorous, but they return a decent rate, are low risk (often FDIC insured), and are certainly nothing to sneeze at.

One other thing to consider, if you haven't already, is some sort of disability insurance. Your ability to work is your greatest asset, especially when you are first starting out. Again, disability insurance isn't at all glamorous, but it can really save the day when you need it. The folks over at the Insurance board can give you more details about where to look, how much to buy, etc. -JG3