The information below is from Suite100.com:
They recommend starting seeds 4 to 6 weeks before the date to set out plants.
Very Early: 4-6 wks before the date of last frost. March 16th to March 30th.
Asparagus, broccoli, cabbage, cauliflower, lettuce, onions, peas, radishes, spinach, turnips.
Beets, carrots, chard, mustard, potatoes.
Average: On or just after date of last frost April 20th. (WSU extension states set out tomatoes Mid May)
Beans, corn, tomato.
Late: One or more weeks after date of last frost April 27th.
Cucumbers, eggplant, melons, okra, peppers, squash.
To find date of last frost, check farmer's almanac here. For Vancouver WA, date of last frost is April 20th. (Date of first frost is given as Oct 15th). That's interesting, because for Seattle, date of last frost is March 10th, and for Portland, which is next door, date of last frost is March 23.
For starting seeds, then, we would time our starts 2 to 4 weeks before planting dates.
Tomatoes - start seeds March 16th to March 30th.
Peppers, cucumbers, eggplants, squash - start seeds March 23rd to April 6th.
I'm not sure about the beans, because they grow so fast and need warm soil. I'm tempted to say start them in May.
For direct sowing of seeds in the yard, zone 8, this site recommends:
Carrots: Feb through April
Lettuce: Feb through March
Onions: Dec through Feb
Peas: Feb through March
Radishes: Feb through April
Spinach: Feb through April
Beans: March through August
These seem early! I'll need to check some other sites as well.
We should be about the same as western valleys of Oregon - maybe a week later. So from OR state extension service, this site:
Beans: May through July
Carrots: March through July 15th
Corn: April through June
Garlic: Sept through Feb (interesting)
Peas: Feb through May
Radish: March through Sept