I think that this website is one of the best around for C25K graduates to consider/use mcmillanrunning.com/tips --in conjunction with his training calculator mcmillanrunning.com/ It is quite a complete website with videos , calculator and lots of good articles. No free training plans however.
I have noted elsewhere that there is lot of misunderstanding about running training - partly due to the use of different terms by different people.
For my purposes - I have personally distilled it all down to a small number of different kind of training runs.
1. EASY - are short and slow EASY runs - done not much faster than walking pace, at a conversational level of effort - and done on days when you are resting from a previous hard day and/or aren't really feeling up to another hard day.
2. LONG runs - are long and slow EASY runs - also done at a conversational level of effort. Because they are LONG, they are either moderately hard or hard runs, depending on length - and need a long recovery afterwards.
3. TEMPO/THRESHOLD runs are runs up to about 20 minutes or so - or repeated shorter times with rest periods between - done at a "comfortably" HARD level of effort. Hence they are "hard" but comfortable in the sense that you can do them for 20 minutes or a number of shorter repeats.
4 . SPEED sessions - probably what most of us think of as "intervals" - uncomfortably HARD but short runs with a longer rest interval between repeats . These can be damaging to people whose muscles/ligaments etc are not strong - and a good long warmup is needed before doing them.
5 HILL sessions - medium length and fast sessions uphill one way ( for maybe 1-200 metres) and a slow walk/jog back down the hill before repeating a few times.