Getting a jump on spring...starting seeds

I'm wondering what veggies I need to start indoors and when?  I've heard hot peppers should be started around this time of year, followed by sweet peppers in a week or two, then tomatoes a week or two after that.  

Do you have a tried & true planting timeline that ends with the historical last frost date?  

What seeds can I direct plant before the last frost date?  I have a cold hardy sweet corn that worked well last year (40's-50's), and claims to be able to survive direct sowing 4 weeks before last frost.  

How about alliums?  I know garlic works, but what about onion seeds?

Carrots?  Beets?  Radishes?  Peas?  

Unfortunately there's no blanket answer.  It depends on your weather. Frost dates and how long your growing season is makes all the difference. I'm in N. California, I have to plant peas, carrots, brassica, cabbage, onions and garlic in the fall and winter, or they won't grow. Too hot.  
As far as seed starting your seed packets will tell you when you should start the seeds. Just find your last frost date and figure out when you should start the seeds inside.  I find a heat mat helps a lot when starting pepper. Other than that I never had any trouble starting seeds inside. A grow light makes a huge difference.
I enjoy starting seeds inside, but hate the hardening off process. It's very hard to do correct when you work.  They say 3 days in overcast will work, but that is rare in the spring where I live.  So I direct plant if at all possible.
Good luck to you.  Have fun.

Thank you.   I do have heat mats, a grow light, a place to start them indoors, & am familiar with the directions on seed packets.  I've always purchased my peppers & tomatoes as transplants, & onions as sets. This is my first time trying to start them all from saved/ traded seed, & I may have to travel for work in the near future.  So, I was hoping to glean a bit of experience to apply toward my planting plans in case I'm not around to tend to the garden as frequently.  

I've found you really can't start your tomatoes and peppers and eggplants too soon. They are perennials and like the extra time. The limiting factor is having room for pots that have enough space for the roots but the easiest space saving container I've planted them in are half gallon paper milk cartons.

I start them in shallow treats since they are easier to warm but transplant them to big containers when they are a few inches high. The roots can grow deep in the milk cartons.  And they aren't too wide so you can have a bunch really close together since they are squares. The only difficulty is when you have to gently untangle the leaves and vines when you are ready to cart them outside.

I live in western Oregon where we have a fairly mild winter and not a hot summer.

I will be planting all my peppers and all my tomatoes during the next 3 weeks. They won't be set out until May (except inside the greenhouse). Whether it is the beginning, middle, or end of May will depend on how the spring goes and what the weather is like.

Any of the "cool weather" crops can be planted before your last frost date, but how early will depend on how cold it gets for you. Here's info from the Southern Exposure Seed Exchange that may be helpful:

Hardiness varies between varieties, health of the plant/soil, windchill, mulch, and microclimates.
Plants will handle a slow decline in temperatures better than a sudden drop to 20F.  
Young plants (particularly greens) may handle low temperatures better as they’re more compact and hugging the ground.

Arugula - 22F. Even’ Star Winter Arugula - 6F
Beets - 20F
Broccoli - 28F for flower heads, 15F for leaves
Cabbage - 20-25F
Carrots - 12F
Cauliflower - 32F for flower heads, 15F for leaves
Celeriac - 20F
Celtuce - 20F
Chervil - 25F
Cilantro - 15F
Collards - 12F
Dill - 25F
Endive, Escarole - 25F or lower
Garlic - 5F if not too much top growth. Frost damage to leaves will stunt the bulb growth.
Kale - 12-15F. Even’ Star Smooth Kale - 6F
Kohlrabi - 20F
Lettuce - 25F for large, established plants. 15F for smaller leaves. Red lettuces look better in winter, as the cold temperatures intensify the red color, while green lettuces tend to look yellow and sickly.
Mustards - 25F
Oats - 20F
Onions, green - 25F
Parsley - 20F for flat, 15F for curly
Parsnip - 0F
Radicchio - 25F
Radish - 20F
Rhubarb - 22F
Rutabaga - 15-20F
Salad Burnet - 0F
Salsify - 0F
Scallion - 25F
Senposai - 15F (Mine died around 25F in late winter, though it survived the first couple of 25F in winter.)
Spinach - 10-15F, Savoy spinach is hardier than flat-leafed varieties
Swiss Chard - 25F
Tatsoi - 15F
Turnip - 20F

Wow!  Thanks Nikki, very helpful resource!

I would really like to just sow seed directly in the ground & cover with a layer of straw around the end of January-beginning of February (Zone 6) (Last frost date April 19).  I already have many winter squash seeds in the plot, but I think by the time favorable germination temps get here, the voles/mice will have eaten them all.  So, I'm trying to get something/anything edible planted that will not need tending to for about 4 months.

I am trying to build up my seed stores as well, so I may start with more mature things like store bought garlic cloves, large beets, radishes, carrots, potatoes, and onions.  I have divided store bought garlic bulbs before into cloves for planting with success, along with potatoes that have grown eyes.  I've not tried growing other mature produce in the garden before, but see no reason why it wouldn't work if there are roots &/or top crowns on the produce.  Plus, carrots, beets, & radishes should produce the seeds I want since this will be their 2nd year of growth.  I have had tomato volunteers before, so I might try some direct seeded tomatoes & peppers to see if anything comes up.  

Cy Cobb wrote: I've always purchased my peppers & tomatoes as transplants, & onions as sets.

Cy, this is great experience to build on. If you've done transplants a few years, you know when you normally put these plants in the ground and what size they should be. So now, you just count backwards from that date to start peppers and tomatoes indoors, with the goal of getting them up to transplant size in time. You're basically just growing your own transplants, instead of letting the grower/store do that.

You can start sooner, but as Jenny noted, space becomes the limiting factor.

I aim to grow about a dozen pepper and a dozen tomato plants each year, so I seed-start twice that many and give away the extras. I germinate in a 72-cell tray, and then pot up to 12oz plastic cups.* I added a real grow light a couple years ago, and got massive growth way quicker than I was used to! They were getting cramped, waiting for safe weather. I put them in the garden early, and almost lost everything to an unexpected late freeze. Lesson learned!

So I actually adjusted my schedule, and now I start them later than I used to. I sew peppers 8 weeks before my frost date, and tomatoes 6 weeks before. Under a proper grow light and good potting mix, they'll get up around 8" tall with several sets of true leaves and not root bound in the cups. If I started them sooner, I'd have to pot them up (more work and more potting mix). Then I'd need another grow light ($$) or I'd need to grow fewer plants. And the longer they're indoors, the more likely I'll get interrupted and fail to water them.

I haven't had success with onions yet. I think the path from seed to transplant is longer, and I just haven't gotten the timing right yet.

This reverse-engineering approach works with direct-sowing too. One year I found a few daikon radish growing on the side of the road, a few blocks from my house. It was late December, I couldn't believe it. I'd tried to grow them in spring several times and failed. So I counted backwards ~100 days, and figured out roughly when they must've been fall-planted. Every year since, I've direct-sown on that fall date and got massive daikon radishes.

*Regarding the cups, these are upcycled from restaurants and breweries. If we go out, and I suspect the establishment doesn't recycle, I grab all the cups from my table and bring them home with me. My friends are used to it, lol. I rinse them and drill a big drainage hole. They last for years, and I can give away extra plants without needed to get the cups back.