Expect temperature at depth (wrecks, underwater canyon) between 55 and 58
degrees F and surface temperature between 59 and 62 degrees F.  A 7 mm
one-piece wetsuit with hooded vest works well for many.  A drysuit is nice
but not required.

More info on San Diego diving, including dive reports, at www.divebums.com

e-shark's suggestion for the divebums website is the best single
source of diving information about San Diego.

As for shops, I'm not sure what you're asking about. For shore diving,
you're on your own except for renting gear, and I can't think of any
shop I'd suggest avoiding for that purpose. As much as I hate them,
Sports Chalet is probably a reasonable place to rent just because
they're big, they've got lots of rental inventory, and they're open
late.

Boat diving is especially popular in San Diego because of the very
short travel times between the dock and the dive sites (almost all are
less than 30 minutes, except for the Coronado Islands). Most of the
charter fleets are running a weekend only schedule through Memorial
Day, so getting out during the week can be a challenge. Call ahead and
see what's available. My favorite boat is the Lois Ann, followed by
Blue Escape/Blue Explorer. However, all the boats do a good job of
helping the out of town diver get the most out of the dive trip. All
of them also have rental gear.

Alan