Job seekers, fire up your resumes. Glassdoor has released its annual list of the 50 best small and medium employers for 2015, rated by employees on company culture, pay, benefits, opportunity for advancement, management, and perhaps most important, whether they would recommend the company to a friend. For the second year in a row, The Motley Fool takes the top spot on the list for companies with fewer than 1,000 employees. (Full disclosure: I'm writing for them even as you read this.) Software and consulting firms Fast Enterprises and Evolent Health take the No. 2 and No. 3 spots, and National Public Radio makes its first appearance on the list at No. 44.

Some 125,000 U.S. companies were in the running this year, based on anonymous reviews by Glassdoor members posted between November 2013 and November 2014. What makes these companies great, according to their employees? There are some common threads in the winners' reviews.

People power
Many reviewers cited the people they work with as part of what makes their workplace great. "Lunch time puts you next to the best conversationalists in the world," wrote an NPR employee in Washington, D.C. Whether it's smart coworkers, motivated team members, or management that takes a personal interest in the rank and file, the right people are a big part of what makes a winning company.

Compelling culture
Reviewers also cited a strong and positive company culture among the reasons they're happy at work. Obviously, having the right people on board goes a long way toward fostering a good culture, but having the right things to do matters as well.

"We're given the autonomy and flexibility to do what we do best toward a purpose we believe in," said Lee Burbage, The Motley Fool's chief people officer and coach. "We prioritize our work around these objectives, and that results in motivated people who produce incredible work. Every company should have a clear idea of what engages their workforce."

Motivating mission
That engagement is crucial to being the best. A positive atmosphere is good, but sometimes we all need a bit more motivation to start the workday. This year's winning companies all offer a sense of mission, a compelling reason why employees need to get to work and bring their best ideas to the table. For workers at The Motley Fool, it's helping the world invest better.

"The Fool draws people from so many diverse backgrounds, but we're uniquely united by what brings us to work here every day," Burbage said. "We're passionate about our purpose and believe in the work we do." A registered dietitian with Evolent, a health care consulting and software firm, seconds that approach. "Everyone seems to be excited to show up to work and is enthusiastic about what they do. There is a strong sense of teamwork."

Appealing perks
No discussion of the best employers is complete without a look at the perks they provide. Reviewers at The Motley Fool and Evolent listed treadmill desks as a favorite perk, allowing workers to avoid some of the health risks of sitting all day. The Fool also eschews a traditional vacation policy, which reduces record-keeping expenses and gives workers the autonomy to decide when they'll be out of the office.

Treadmill desks are an expensive perk at an average cost of $1,400 per workstation, but Burbage says the real payoff to investing in such items is demonstrating responsiveness to employees' requests. "Benefits like treadmill desks, spinning classes, and quiet rooms let Fools know that we're listening to their ever-changing needs and we're engaged in their overall happiness," Burbage said. "We don't believe perks drive our employee engagement, but feeling like your leadership team cares about you and what you want or need to be happy does drive engagement."

Other perks are built into the job. Fast Enterprises works with governments across the planet, which means employees have a "great opportunity to see different parts of the country and world," according to a Denver-based implementation consultant for the company.

Worth watching
Fifth-rated TubeMogul(TUBE), a video ad software company, and No. 14 MobileIron(MOBL), which develops mobile IT software, went public earlier this year. Most of the other companies on this year's SMB list from Glassdoor are privately held, and many are start-ups. That means this list is worth watching for IPO-minded investors as well as for job seekers who want a winning work environment.