I use OE for my equipment needs, never tried any of the stores so I can't really comment other than to say that I'm always satisfied.
I'd suggest a shore dive at La Jolla Cove (little underwater reserve) as a simple, interesting dive (rocky reef, kelp forest, max depth around 45ft within the reserve, surface is monitored by lifeguards).
If you can get a local to go with you, try Children's Pool, currently home to a large and friend harbor seal colony. You are likely to be played with during the entire dive. A note of caution: seal activists actively dissuade the public from going onto the sand and will usually convince people it is illegal to do so. This is not true, and the lifeguards will tell you the beach is open but try not to scare the seals on the way into the water (and keep the activists relatively under control).
A dive I like is a night dive off La Jolla Shores. A long swim gets you to the beginnings of a submarine canyon. Very common to dive along the "wall" (really just an 8ft ledge) at about 65ft. Much better at night, more stuff.
Try this website for lots more information, and an e-mail list full of local dive buddies:
Divebums - A San Diego Dive Website
Enjoy!
PS: Oh and conditions... get on the divebums email list for constant dive reports. Some places can get quite surge-y or unpleasant without seeming to be all that bad from the parking lot, so I'd suggest asking a local how things look the day before you go. Generally you are looking at mid-50s at depth, with 5-30ft viz. I dive wet, 7mm with hood is the bare minimum.