These are some things we've found useful and you might too. All of these resources are free, or have a useful free version, unless otherwise noted.
Vlambeer Toolkit - A great list of resources for indie developers.
Juice It or Lose It - This is a fantastic talk by Martin Jonasson & Petri Purho that illustrates how simple tweaks can have a huge impact on the feel of a game.
Trello - A streamlined project management web app.
Toggl - Simple time tracking web app.
HelloSign - Convenient tool for electronically signing documents. Great for contracts and other business related documents.
SourceTree - GUI client for Git or Mecurial.
Unity - Game development engine with support for many platforms.
Visual Studio Code - A lightweight general purpose text editor (well, sort of an IDE lite). If you don't like IDEs this is a great replacement for Visual Studio proper. (Yes, the naming is confusing, but it's totally seperate from Visual Studio.)
dotPeek - .NET decompiler that's great for digging a little bit deeper into the libraries you use.
Freesound - Database of audio samples released under Creative Commons licenses that allow reuse.
Events and Communities
Boston Unity Group (Boston/Cambridge) - B.U.G. is a monthly gathering of Unity developers in the Boston area. A super cool meetup, very informative and welcoming to newcomers at all skill levels.
Boston Festival of Indie Games (Boston/Cambridge) - Boston FIG is a fun one-day festival with a showcase of independent games and informative talks. Held each fall on the MIT campus. Admission for this one is super cheap (about $10).
Pioneer Valley Game Developers - (Pioneer Valley) Western Massachusetts group hosting informative presentions, networking and gaming events. Their events are always fun and welcoming to newcomers.
IndieCade East (NYC) - International Festival of Independent Games, New York City edition. Smaller than the West Coast original, but with plenty of games, unusual exhibits, talks, and social events. Three-day event held around Valentine's Day each year. Not free (about $100 for all three days).
One Game a Month (online) - Challenges you to create one game every month for a year.