Torrey Pines is the most hiked trail on the coast, if I recall. It is nice out there. There is also Florida Canyon in the middle of SD, and another canyon that is nice right in Mira Mesa. Check them out.
There's some AMAZING hikes down through out the 78 up between Escondido and Ramona. A great book to have on hand to find all these trails is called "60 Hikes within 60 Miles". i'm attaching a link to it. Mt Woodson is a really nice hike, I live at the base of the mountain there. It can connect with the Blue Sky reserve that takes you around Lake Poway (takes you up the backside of Mt Woodson). I love to hike (if you couldn't tell) so I hope this bit of info is helpful.