When should I plant outside?

[originalmj]

I'm working on my first vegetable garden. I built two raised beds and filled them with a mixture of vermiculite, compost and peat moss. My seedlings are started inside and some are looking stronger than others. I'm wondering when I should put them outside. I live on the zone 5B-6 line. The last frost date is predicted to be May 24th, but it has been pretty warm, though today it is 50 degrees. No frost on the grass in the morning. The seed packet directions have no mention of starting seeds indoors, but the garden center said that in this zone, if you don't start indoors, you won't harvest before frost in the fall.
Here's what I have started inside:
Spinach
Lettuce
Peppers
Basil
Parsley
Beans
Squash
I also have seedlings for a whole bunch of annual flowers

I also want to plant onions- not sure when to plant those either?

When should I move the seedlings outside?