One of the resources I come back to time and again for advice on when to plant is the Vegetable Planting Guide (PDF file) published by the UC Vegetable Research and Information Center and UC Davis Plant Sciences. It's a handy little chart showing when to direct sow and transplant various vegetables all year round in the greater Sacramento area. Even though I've gardened for years, I refer to the chart often, especially when I'm planting a veggie that's new to me.
Melons, squash (winter and summer), cucumbers, green beans and corn can all still be direct seeded into the dirt and will germinate quickly in this hot weather. In fact, green beans and corn grow so quickly they can be direct sown through June around here since our warm weather lasts well into the fall. This corn was planted in the backyard only about a week ago and is already a few inches high:
It's also not too late for heat-loving plants like eggplants and peppers, but you'll need transplants rather than seed. Both eggplants and peppers take a long time to germinate. Tomatoes ideally went in the ground last month (I even planted some in mid-March, which was a risk I'm willing to take and which paid off this year), but I'd still try planting tomatoes as long as you have relatively mature transplants. Stick to fast growing varieties like cherry tomatoes, and stay away from the large-fruited heirloom varieties that take more time to bear ripe fruit.
So, what are you going to plant this week?