I have dove there on 3 or 4 occasions always around the end of June and first week of July.
The last time I dove there on July 1st 2002 the temp was 54 Suunto degrees.
Point Lobos is a must, as are reservations.
Monastery and Spanish Bay Beach is a signature dive for the area as is Point Lobos. This is an advanced and deep dive and the recommended exit is on hands and knees referred to locally as the monastery crawl. Deep underwater canyon with nutrient rich cold water comes in close to shore. Waves rise up suddenly and flop over and have killed those who attempted to walk out. So like any beach dive, know conditions and local recommendations. The locals in the NoCAL forum will tell you more about this wonderful site.
There are many excellent dives in Monterey, the kelp, otters, and harbor seals all make for a great dive from beach or boat. Water will be about 52F or so in July so you can adjust from there. Winter is 45-48. Most wear dry suits or wetsuits with a core warmer (spring suit) over it. Dive shops are like gas stations in Monterey, one every other block. They even have a little cart that comes to the beach and picks up your tanks for refills. A very dive friendly town (they know a good tourist $ when they see one). Parking meters vigorously enforced.
Dives I would go for:
Point Lobos
http://pt-lobos.parks.state.ca.us/scuba/scuba.shtml Reservation required as is a partner when you enter the park.
Monastery
Spanish Bay
Lovers
Any place there is ocean, there is good diving there. Kelp is everywhere. Buy a Frankos map when you get there. There are local un-posted restrictions on some dive sites about when you can and can not dive (lovers cove for example)..
I would skip the break water where all the classes are held.
The Monterey Aquarium is a must see and an all day thing.
Do not forget the 17 mile drive through the giant redwoods and $$$$$ houses, past Spyglass and Pebble beach. Carmel by the bay is right there too. So is the former Ft. Ord where I went to Basic back in 1972 (a little history there) when the Aquarium was really a cannery and a very rough neighborhood. They really cleaned it up.
I would highly recommend you take the coast (route 1) out of San Louis Obisbo. It takes a little longer, but worth it, Big Sur and all.
Swell Model (note big swell is the norm there, dive early am)
http://www.garlic.com/~triblet/swell/wamglance.html
http://cdip.ucsd.edu/recent/model_images/monterey.png
Local dive operations:
http://www.mantaraydive.com/
http://www.cypresscharters.com/
http://www.montereyexpress.com/
Local Dive Forum:
http://groups.yahoo.com/group/ba_diving/
Where to stay, I stay on the Army base for under $40.00 - but you will have to stay off post at a hotel. Best Western there is not bad. No real recommendation there. Cost is over $100.00 a night. The dive shops have links to local hotels too. Local towns are Monterey, Pacific Grove (on the water) Carmel by the Sea and Sea Side (short drive and outside the gates of Ft. Ord, not as high class a town).
If you like steak an absolute must do is to go to AJ Spurs Restaurant. They have them near Monterey (someplace, never been to that one) Buellton (on the way to Solvang on the right next to the car dealership) and Templeton (10 miles south of Paso Robles, in the center of town all two blocks of town) Stop at Buellton at AJ Spurs Restaurant. I will guarantee it to be the best steak you have ever eaten and at less than $20.00 per plate a very reasonable and full meal (vaqueros soup [excellent], fried potatoes and onions, steak, salad, liqueur or root beer float $19.95) before 5:00 it is $13.00 for the Filet Minion and $11 for the Sirloin (what I usually get). My wife had the filet last time and.... well you just have to stop for a steak at AJ Spurs. We drive to Buellton to steak every so often, it is that good. At Carpinteria (south of Santa Barbara) is a good place to eat dinner (opens at $5.00) called Clementines if I remember right. In an old house, serve complete meals including pie made onsite for a reasonable price and not a bad steak