Having a source control system is a must these days, but I must say that coupling that with a continuous integration (CI) build system is just as important. It's really frustrating to pull the supposedly latest or most recent 'stable' or 'production' version of code from source control then still be unable to compile and/or execute it due to human error. A continuous integration build server makes that impossible by demonstrating that the source can be used to build a usable system.