the way I do, is whatever you want to grow find out the number of days to maturity, then find out what the 1st average frost is in your area, if whatever you want to grow has 70 days to maturity, then count back 70 days from the 1st frost date. if it turns out you have 80 days to frost then you can plant it
I used to live up in Seattle and would sometimes plant a 2 batch of seeds around mid/late June. usually not the cooler weather crops like lettuce or peas as the weather woudl "Sometimes" get too warm in July for that (hard to tell with Seattle though), but beans, carrots, beets, tomatos, cucs, zucchini, etc. would usually be just fine. maybe heading over to molbaks (my favorite store in the world!) for some starts would be a good idea too.
Great ideas from the others! You could also check with your local agricultural dept/county extension office (even on-line) of what will grow best in your area & when to plant. Also, GrowVeg.com....LOVE IT! This planner is how I began my garden. Check the Almanac website, which has great information. Just plug in your location and you will have a list of vegetables/fruits/herbs that you can plant. Good Luck & Happy Planting
You can actually start beans, okra, broccoli, cabbage, and many others right now. Cmpenley is right on about a farmers almanac. You should check out usagardener.com. They have lots of good information. With the early warm weather that we had in Washington, DC I noticed that my strawberry plants are already done for the season. Hope that helps.
you should still be able to get beets,beans,carrots,turnips going this late and another chance to plant peas in late july. but in late july early august if you have a raised bed or two then you can plant collards for fall crop and at the end of august you can plant lettuce and spinach as long as you do a tunnel cover over the bed and in very early spring you will have fresh lettuce and spinach if you do both. I did this last year and had fresh lettuce in late feb. in western washington state near hood canal area.