Are you hiring noobs straight out of college or seasoned pros? And I assume you're asking what would a developer want as opposed to what's cost effective for the company.
Perks like a foosball table, ping pong table, free snacks / drinks, free lunches, company-branded merchandise (e.g. shirts, pens) etc. cost the company relatively little and are almost considered a baseline now. That might be enough to draw in the juniors.
If you're hiring senior developers... they're older. Have families, etc. Consider offering things like flexible work hours, option to work remotely at least part time, more vacation time (or earn more in later years), retirement assistance (401K matching in US, RRSP matching in Canada, etc), profit sharing, family Christmas / holiday-of-your-choice party where the kids of employees are invited, etc.
It's also nice to see a company that pays for books, conferences, etc.
Avoid unlimited vacation policies. That's a big red flag.
A private office would be an amazing perk but is almost never offered (because floor space is expensive). But a cubicle would usually suffice. I don't know why cubicles get such a bad rap. They're ideal for developers. Any company that happily promotes an Open Floor Space is either clueless or lying to you -- if you happen to have an open floor concept, a GREAT perk would be a pair of good-quality noise-cancelling headphones.