We've collected links to free 5k training schedules from all over the internet in one place, and personally used the training schedules from Hal Higdon for several races.
Hal Higdon 5k Training Plans
Each of these plans is an 8 week 5k training schedule
Jeff Galloway 5k Training Schedule
This training schedule is a 15 week 5k training schedule
Cool Running 5k Training Plans
Each of these plans is an 12 week 5k training schedule
Mayo Clinic 5k Training Schdule
A 7 week 5k training schedule from the Mayo Clinic
About.com 5k Training Schdule
An 8 week 5k training schedule from About.com