When thinking about perks, in my opinion, it should be something which boosts motivation strongly in the short-run and keeps it up in the long-run. At the same time, you should try to have a benefit, too. But don't tell the new developers about your benefits ;)
Short-run boosts might include giving away physical gifts. Hashnode employees get a free Amazon Kindl, which sounds awesome! It has the secondary effect that they all have a gadget to read ebooks comfortably in order to improve their knowledge (or read a nice fantasy novel to chill out before going to sleep, which is important, too).
Depending on your funds and company, you might also give out a new laptop as a gift, which they have to use for work, too. They get new tech and you are freed from maintaining it. Think about renewing the laptop every 4 years or so in order to keep the employees productive with a good computer.
As for long-term boosts, tell them about your great working conditions! Reading the Hashnode perks, I wonder why I have to pay for my coffee and lunch and still work for that company :D Especially for developers, coffee is really important, so provide it either for free or make sure that they only have to pay very very very little.
Tell them that you care about them! Tell them you will give them free work-related ebooks (which they can read on their Kindl). Tell them that you will send them to conferences and conventions. They have to get the feeling that they don't only work for you, but that they can also grow their career while doing so. We had some discussions about that not too long ago, and I proposed changing jobs every three years, ideally staying within the company. Your task is to make them stay with you on your team! Make them feel they do a diversity of things, that they are responsible/important and don't have to go away with their knowledge in order to gain further experience.
Last, but not least, satisfy the social factor. Organize bowling events, after-work parties, sports teams (like going jogging every Wednesday after work), etc. It's important that, at work, you are the boss, you make firm decisions, you consider your employees opinion (but do not just let them decide, that's your part; except for delegated work) and everyone respects you. However, when work is over, your relationship has to change. People want to forget about work and chill in the evening. Be a comrade. Talk to them about their families, hobbies, sports and genuinely have fun. It is not easy to balance that kind of relationship, but at least two of four department chiefs at my working place manage to do it, so I am sure you can, too :)
Those are the kind of perks I would want to see when applying for a job at a new company. I think, it's also about what the Silicon Valley companies use. Just think of the new Google Campus. They have everything there. Plazas for Yoga, bike tracks, cafés, just next to the offices. Employees usually get anything they need to be productive and keep up motivation. That's why a lot of people hype it (even though it comes with 0 away-from-work-time and those people probably work a lot more hours for the same or less money than I get, relative to the region).