Everyone needs to have a pile of savings -- but not all savings are the same. To put your savings into context, think of your finances as a wedding cake.
The bottom layer is your long-term savings. The goal is to compound that long-term money into a wide, deep foundation of your finances. Ideally, it will eventually be the biggest piece of your cake, broad enough to support a long and active retirement. Stocks of solid, long-term growing companies are ideal for this -- think Wal-Mart
Intermediate-term savings make up the ingredients of the second tier of the cake. This is the big-ticket fund you plan to spend within about five years. It might be five years' worth of living expenses if you are already retired, a college fund if you have older kids, or a house down payment. This is also where you stash money earmarked for the new roof, new car, or even a major vacation. CDs or short-term bonds can be used for these predictable expenses. Being the middle tier, it should be accessible sooner than the stuff in the bottom layer, but not until the proper time.
The top tier of the cake is your rainy-day fund, your peace-of-mind money. It's there for medical emergencies, car-repair emergencies, pink-slip emergencies. Think of it as the credit card-avoidance fund, if you like. This money needs to be readily available -- but not too readily available, if you know what we mean. A money market account with check-writing privileges would be a good place to keep it, but your everyday checking account probably would not. You don't want to start thinking that a trip to Cancun is an emergency.