Scott's right about Laguna Being the best option. The drive is a little ways so you'll want to give yourself some extra time to get there and back but this time of year parking tends to be fairly easy if you're there before 8 at some fo the less direct entry spots.
Early in the morning it isn't a bad drive at all. I "enjoy" the disneyland fireworks every night from my apartment, and if I leave at 6am, I'll pick up my dive buddy and be at Laguna beach by 6:30am and in the water by 7am, then back home by 9am after dropping off my dive buddy and his gear. All this while nearly driving the speed limit (+5).
I prefer to dive the west side of Crescent Bay, of all the sites at Laguna beach, it's the most southern facing beach. If the surf at Crescent is bad, you're not going to want to even think about anywhere else
Oh and if you do decide to go to Crescent, the stairs on the west end off of Circle Way (street) are a lot better than walking up the ramp off of Cliff Dr.
NOTE: there is a little market across the street of Cliff Dr on PCH for the after dive snacks.
Getting there:
I-5 South, 55 South, 73 South, exit McArthur Blvd, and take McArthur to Pacific Coast Hwy, turn left and cruise down about 5 miles to Cliff Drive. Turn right on Cliff, then turn right agian onto Circle Way, then follow it around and park by the stairs.
Coming Back:
Because PCH starts to populate with all the weekend Ferrari, Lambo, Masterati, and Porsche owners, I go a slightly different route back home. Instead of taking PCH all the way to McArthur Blvd, I go around slightly.
From Circle Way, turn left on Cliff Dr, then turn left on PCH (pacific coast highway) for about 3 miles to Newport Coast Dr and turn right, after you go all the way up the BIG hill, you'll turn left on San Joaquin Hills Rd, and take that down to McArthur Blvd. Turn right on McArthur Blvd and take it to the 73 North, then the 55 North, then the 5 North. YAY.
NOTE: You can get into the 55 North Car pool and stay in it to the I-5 and to Disney Drive all from the car pool, for ease of avoiding annoying, hot tempered, stupidly fast paced, cranky California drivers.
