You're in the same zone (8B) as we are here in central Texas though I suspect that you have cooler nights than we do, and your first freeze data (if there is such a thing in Santa Clarita) is probably later than ours.

Right now, we could potentially plant winter squash and melons. I have planted some recently, and so far so good. It's a little late for sweet potatoes for us, but your season is probably longer. I actually plan on planting a few late sweet potatoes to see how they do - will probably have to protect with covers once it gets close to first frost date. You could also choose a relatively quick-growing sweet potato variety.

Here we would not plant regular potatoes just yet - next month would be better.

Right now with many days of temperatures over 100 F, the only things I am planting are okra, black-eyed peas, and hot-weather specialty greens such as molokhia, vegetable amaranth, and purslane. Will be planting other things in August-October; many other choices will be in planting season then for a fall crop.

Try checking a state or county agriculture website to see if the have a planting guide for your area

Here is a link that might be useful: cajunkorner

JD~ Along with c_penton's suggestion of checking out your county ag. site, check out what's selling at a nursery by you (a nursery, not Lowe's, HD etc). Someone in charge at the nursery will (should) know what will work for your area.

Here is a link that might be useful: Gardening With Care

Two of my summer favorites are beans (bush or pole) or swiss chard. Don't know if it's too hot in your zone for those now.

Also, if you have a farmer's market near you, the people manning the booths there will know. The one near me is only selling what needs to be planted at the correct time of year.

Here is the planting schedule I use in Travis County, Texas, which is also zone 8b like where you are:

http://www.co.travis.tx.us/agext/garden/veggies/planting/default.asp

I also use a print publication from the Travis County Master Gardeners, which includes flowers and herbs as well as vegetables.

For Los Angeles County, the following links appear to be helpful:

Garden tips for planting and other activities by month and season
http://celosangeles.ucdavis.edu/Common_Ground_Garden_Program/Garden_Tips_for_Los_Angeles_County.htm

Gardening articles, including Burpee guide for planting seeds in California
http://celosangeles.ucdavis.edu/Common_Ground_Garden_Program/Gardening_Articles.htm