There are pros and cons to an immediate annuity.
If the annuity payments are guaranteed for both your lives (a joint and survivor option) then as long as the insurance company remains solvent you will be guaranteed to receive this income for the rest of your lives. There are no other investents that can provide such a guarantee.
However, if you need additional funds in the future you will not be able to withdraw it from the annuity as this option is not available after a contract is annuitized. In addition, your annual income is fixed and will not increase with inflation as other types of investments may be able to provide for increases.
http://www.bankrate.com/brm/news/dollardiva/20000608b.asp
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