Right now Certificates of Deposit (CD's) pay pretty low interest rates. You'd do pretty good to get a CD paying over 2% and shorter term CDs pay a fraction of a percent. In years past when interest rates were higher CDs paid a lot better.
Mortgage-x website has data on historical mortgage indexes. One of the indexes is the Certificate of Deposit Index (CODI) Mortgage-x defines it as "The Certificate of Deposit Index (CODI) is the 12 month average* of the monthly average yields on the nationally published 3-Month Certificate of Deposit rates. "
I got the CODI numbers from their current index lists and their historical CODI data.
Here's a chart showing the interest rates from 1967 to 2010.
I am only showing the rate for the month of January of each year just to keep the chart less cluttered. There is some fluctuation in rates month to month but mostly they are gradually drifting up or down. Showing January rates only is pretty representative for the long term trend. If you want you can see the monthly data on the Mortgage-x website.