When you meet someone and get them interested in you they become part of your personal network. If you go long enough without contacting them they will leave your network. Facebook and LinkedIn are dedicated to helping you solve this problem. An email every now and then goes a long way too.
When you do contact someone make it personal. Show them you were thinking about them. Sending all of your friends a bulk email will make them more likely to lose interest in you.
Creating your network is not something to do overnight. It takes years to meet people and build relationships. Plan ahead and create options for yourself before you need them. Get out and meet new people in the industry. Whenever you meet someone new take a moment to get to know them. Once you have met someone maintain the relationship. The software industry is a small world and you never know who you will run into in the future.
However, you can’t always have a personal recommendation. There are a few other models you can follow to help companies find out about you and gain enough trust to offer you a job.