I recently spoke with my investor today. Ironic I asked the same questions because I was trying to decide which path to go.
What my investor broker explained to me... CD is locked for certain term and can be renewed at end of term. Tend to have 2-4% returns in long run. If you take out early, pentalty have depend on which company.
INGdirect.com
AMtrustdirect.com
to name few that I have seen good CD rates. You can look at Bank Rates for high yield saving, or cd.
However, if you are going for a long long term like retirement. Go for IRA Roth or Mutual Funds. They yeild 6-8% returns in long run and you can continue to add more fund to it monthly.