Davis Square - In Somerville, this area is one of the cheapest, best places for young professionals to live.

• Diesel Cafe - A massive cafe in the heart of Davis Square, Diesel is an indie, laptop-friendly (power outlets everywhere, no rush to vacate your space) spot with good coffee and great atmosphere. The wifi isn’t free, but for $13 / month, it’s still affordable even if you’re a rice-and-Ramen bootstrapper. I’ve had serendipitous encounters with many startup founders, developers, and other startup folk here.
• If you must have free wifi, or the atmosphere isn’t your thing, there’s a Starbucks right across the street that’s also laptop-friendly.
  

Central Square – Cambridge’s meeting ground between corporate-heavy Kendall and academia-suffused Harvard. There’s cheap living space here, but it’s a bit less safe / less pleasant than Somerville.

• Cafes: Andala Coffee House hosts the weekly startup-focused OpenCoffee meetup, and is a well-used venue for other laptop workers thanks to its free wifi and tasty food.Clear Conscience Cafe, though it only provides free wireless for an hour, is close to the Barron Building, where many startups have their offices.
  

Kendall Square / MIT – Home to some internet heavyweights like Akamai and Endeca, and Cambridge offices for Google, Microsoft, VMware, and many others.

• Coworking: The Cambridge Innovation Center, where many of the big corps have their offices, is also home to the Cambridge Coworking Center. A more networking-focused coworking space, The Venture Cafe, is being tested as a concept here as well.

Reviews courtesy @JayNeely at http://socialstrategist.com/boston-startups-resources/