I graduated from C25K about 6 weeks ago. Since then I've been running regularly, slowly increasing my fitness and on Saturday I did my first ever Parkrun. I have to say that it was great running with all the other participants and I positively flew around the 5km course in 27:44.
So for those of you still working your way through C25K I cannot recommend Parkruns highly enough. They were a great bunch of people and there is no pressure to go round in any particular time - it's up to you how fast you want to go - but what you will get is bags of encouragement and you might find you surprise yourself.
Anyway a really good goal to aim at and to keep your motivation going once you graduate.