From now until Dec. 31, seniors who are eligible for Medicare can sign up for prescription drug coverage or change their existing plan.

"Qualified seniors should not delay," said Peter Pitts, president of the Center for Medicine in the Public Interest. "With hundreds of private plans competing to provide the best deals, Medicare Part D has more options and better coverage than ever before."

Most public health programs are funded and managed by the government. Part D is different because it's administered by private insurance companies. Taxpayer dollars operate as a subsidy, but then seniors are allowed to select the drug benefit that best suits their needs.

"According to a recent Harris Interactive Poll, an overwhelming 87 percent of Part D enrollees are happy with the program," said Pitts. "By leveraging market forces, Part D has both lowered costs and increased choices for seniors."

The program has reduced outof-pocket healthcare expenses for the average enrollee by 17 percent, according to a study published in the Annals of Internal Medicine. The projected cost of Part D to taxpayers over the next decade has dropped $117 billion since last summer, from $915 billion to $798 billion.

Some Medicare plans, especially the more popular ones, will be more expensive in 2009, so even seniors who are pleased with their existing drug coverage should examine the options.