Other offerings, like critical illness and accident policies, help workers offset gaps in their core health and life insurance coverage, such as deductibles, and Covill says these benefits are generating the biggest increase in demand. "Employees are more focused on being good individual risk managers," he says.

"In the last few years, the buzzword has become consumer-driven benefits," says Neicee Durrence, vice president of acquisition strategies at Unum, an insurer that provides a range of voluntary benefits. "Consumers are being asked to fund a greater percentage of their overall benefits package and also make decisions around which products are best for them."

Durrence says the most rapid growth is in critical illness and accident plans. "Healthcare reform is really the driver," she says, and predicts that interest in voluntary benefits will surge as more reforms take effect.

Covill likens the current situation in employee health coverage to the shift from defined-benefit to defined-contribution retirement plans and says healthcare reform will reinforce that evolution. Analysts expect healthcare reform to boost employees' deductibles or out-of-pocket costs, he says, and employees will look to fill those gaps with voluntary benefits.

Employers used to offer voluntary benefits separately from their regular benefits package, but Covill says these days more companies are integrating voluntary and core benefits, using the same technology platform and communications to enroll employees in both. Combining the two types of benefits provides some efficiencies for employers, Covill notes, and may also get them a better deal from their carriers.

For a look at a new model for providing health insurance Aon Hewitt is rolling out for corporate customers, see Early Health Exchange.