They are amazing benefits!
Company covers 100% for individuals and 90% for the rest of the cost of medical plan, which is phenomenal. The medical plans are also top-notch. Unlimited vacation / sick days, and as far as I know no one has any problem taking time off. Company reimburses for lunch on Tuesdays and caters on Wednesdays. Company also treats interviewees and whoever goes to lunch with them. Plenty of snacks, including those from SnackNation. Hours are extremely flexible. Employees are treated as adults who can manage their schedules.
I love that the company made a commitment to the employees to pay 100% of medical coverage for individuals. The family coverage is also excellent, especially given the smaller size of the company. While benefits year to year can change as external factors change, the benefits since I've been at the company have overall been above par for a startup.
List based on reports from current and former employees. It may not be complete.