In reply to ow arm:
Here's some, I actually don't have that many because I only just started using it as I moved to Germany
Rhosgad run trails
http://www.strava.com/activities/54046581
Capel trail trails
http://www.strava.com/activities/19698389
Marchlyn round fell..
http://www.strava.com/activities/22341589
Siabod
http://www.strava.com/activities/22341578
Foel Lus
http://www.strava.com/activities/36783379
For me the best runs are Moel Eilio.. any link on that ridge..
Moelwyns is great, done the race a few times, cracking route..
Carneddau was a great race, now dead I think.. but its essentially the CD > Yr elen horseshoe which has some fantastic running..
the other good area and few visit is north of capel, there's some lovely trails in that area around gerionydd/capel and gwydr forest if the weather is bad..
However I think my favourite run was from rhydd ddu, take the bridleway/path across to beddgelert forest and climb to the col between the he bog satellites and nantlle ridge, run up that shoulder, faint path, then come back along to Y Garn on the nantlle ridge and descend.. its only 5 miles or so, but a cracking route.