Other developers are great people to have as friends. In return, of course, you help them solve their problems, and share your own good advice. Artists are good people to have as friends. Journalists are good people to have as friends. They can offer advice on promoting your products, they can tell you about trends in your part of the industry, they may be willing to write reviews, and they will listen in a most flattering manner to any news or gossip or opinion you can offer in their area of interest.
Webmasters are good people to have as friends.
But mostly, friends are just plain good to have. They're better than money, better than fame. It's the best advice I've got to give you.