You could look at savings bonds-- if you are really willing to keep them 20 years then an EE bond pays 3.4% or so; an ibond has a partially variable interest rate-- has recently been above 1%.
A CD ladder (where a CD matures each year, and you can roll it into a new 5 year CD) can often be a good way to get good yields, although less so lately.
A little less safe, would be a bond fund-- generally higher yields than savings accounts, but the longer the "duration" of the average bond, the risk/reward there is (so a short-term fund usually pays the least but is the safest. intermediate may pay a bit more but fluctuate in value more as well, etc.)
A balanced fund--- mix of stocks and bonds in one fund-- is generally safer than stocks only-- the two will often, although certainly not always, move in opposite directions and cushion each other.