(MONEY Magazine) – Do you harbor the conviction that you -- or your spouse -- will live to see Willard Scott wish you a happy 100th birthday on Today? If longevity seems in the cards or in your genes, you should consider investing some savings or part of a lump sum from a corporate retirement plan in a single-premium immediate annuity. The best of these products, which are sold by insurance companies, offer a higher payout -- as much as 13% for a 65-year-old male -- than most other conservative long-term investments. Annuities make particular sense if your health is good and your ancestors were long-lived. Since monthly payments to you are based on average life expectancy, an annuity turns out to be a terrific deal if you live longer than actuarially expected. Annuities have a major drawback, however: your monthly payment doesn't increase with inflation. Advises Dede Pahl, an academic associate at the College for Financial Planning in Denver: ''No one should put all of their money into an immediate annuity. But people with assets to spare might buy one for steady income and invest the rest to keep pace with inflation.'' If an immediate annuity seems right for you, prepare to do some serious shopping because payout rates vary considerably from one insurance company to the next. For example, a 65-year-old man with $100,000 to invest could collect anywhere from $521 to $1,080 a month for the rest of his life, depending on the contract he buys. Before you start searching for the highest yields, however, you should select a settlement option -- the terms under which income is paid out. That's because a given insurer doesn't necessarily offer competitive payout rates for each settlement option. In general, the size of your monthly check will depend on your age and sex, how much you invest, and whether payments cease at your death or continue for a specified number of years or until the death of your beneficiary. Here's the menu that insurers typically offer: -- A straight-life or lifetime-only annuity pays you until you die, whether you last to 111 or expire shortly after signing the contract. Since straight- life annuities are risky, they come with the highest monthly payments. Indeed, straight-life annuities make sense for people who need lofty monthly incomes and lack dependents or intend to provide for them some other way. -- A life-and-period-certain annuity pays you and a beneficiary for at least a specified number of years, typically 10, 15 or 20. For example, if you buy a 10-year-certain annuity and die after seven years, your beneficiary will receive monthly payments for another three years. But you pay a price for peace of mind. Ten-year-certain contracts usually pay 5% to 8% less than straight-life annuities. -- An installment-refund annuity pays back your original investment to your beneficiary if you die. Installment-refund annuities usually pay 4% to 5% less than the straight-life variety. -- A cash-refund annuity works like the installment-refund type, except that your survivor receives the balance of your premium in a lump sum. The advantage is that your beneficiary can reinvest the cash at current rates. The disadvantage is that cash-refund annuities usually pay 1% to 2% less than the installment type. -- A joint-and-survivor annuity pays until both you and your beneficiary are dead. The amount of your monthly check is based on your survivor's age as well as your own. Insurers generally offer joint-and-survivor annuities that pay 100%, 67% or 50% of your monthly benefit to your survivor. Once you decide on a settlement option, ask two or three insurance agents or brokers for quotes on the type of contract you want. Rates change as often as weekly, so ask for quotes when you're ready to buy. You can get an idea of who pays the highest rates by consulting Best's Retirement Income Guide, a reference book available in most public libraries. Even Houdini could not wriggle out of an annuity contract gone sour. So entrust your nest egg only to an insurer rated A+ or A for financial strength by Best's, particularly if you live in the District of Columbia or one of nine states (Alaska, Arkansas, California, Colorado, Louisiana, New Jersey, Ohio, South Dakota or Wyoming) with no guaranty associations to make good on contracts issued by life insurers who go bust. One comforting note: your heirs get a tax break if you die before recovering all the money you invested in an annuity. The unrecovered amount is deductible on the income tax return that your executor files for you after you're gone.

BOX: Check It Out Some top buys

These insurers offer the highest-paying immediate annuities for a 65-year-old man who invests $100,000, according to Best's Retirement Income Guide. -- Straight life: Federated Life ($1,080 a month; 507-455-5200); Federal Home ($990 a month; 407-345-2600); Lincoln National Life ($979 a month; 800-348-1212) -- 10-year certain: Federated ($934 a month; 507-455-5200); Lincoln National ($930 a month; 800-348-1212); Standard Insurance ($927 a month; 503-248-2700) -- 20-year certain: Standard Insurance ($847 a month; 503-248-2700); Lincoln National ($846 a month; 800-348-1212); United Pacific Life ($840 a month; 215-864-5900) -- Installment refund: Lincoln National ($937 a month; 800-348-1212); Standard Insurance ($935 a month; 503-248-2700); United Pacific ($935 a month; 215-864-5900) -- Cash refund: Lincoln National ($923 a month; 800-348-1212); Manufacturers Life ($913 a month; 416-926-0100); Minnesota Mutual ($904 a month; 612-298-3500)

CHART: NOT AVAILABLE CREDIT: NO CREDIT CAPTION: At a Glance What you can expect to collect This table shows the best and worst monthly payouts available for immediate annuities under five options for men and women ages 65 and 75 who invest $100,000.