Should I order onions for planting this fall?

I believe I'm supposed to have about five weeks left frost free, if this is an average year.
Obviously the onions wouldn't arrive instantly, since I want to order them from some online source - I don't want boring everyone's-gottem onions, I want nice organic onions! Ahem. So, if I got my counter-culture vibbin' onions within the next ten days or so, would it be good to plant them before frost, or should I just wait until next spring?

I'm looking at obtaining either nodding onion (Allium cernuum) or Egyptian onions, (Allium proliferum)

If I shouldn't plant onions, is there something else edible-like that I could try to plant this autumn for production next year? (I already have all the bushes/shrubs/trees I can handle.)

Not sure about onions specifically, but garlic, chives, etc. can be planted in fall and overwinter with absolutely no problem. Of course plant them in an area with decent drainage to avoid rot. I'd imagine onions, like practically all bulbs can be planted in fall with no issues. It's the point of the bulb, energy to get through winter. Ornamental alliums are planted in fall, edible alliums (onions) should follow suite.

Worse comes to worse you lose a bit of money on bulbs, not that big a deal in the long run.

Planting onions in the fall, like other bulb types, will result in a bigger onion to harvest sooner than spring planting will. I say to go for it.

I'm a big fan of yellow potato onions. Order a set or two now and do a seed increase this year and you should be able to meet your onion needs year-round for a long time to come.

We've been growing these for two seasons now: http://www.territorialseed.com/product/Yellow_Multiplier_Onion/ but I want to get some of these to add in this year too: www.southernexposure.com/yellow-potato-onion-8-oz-p-873.html

We're a little south of you, and plant garlic and onions in October, so you should have time to wait for the mail.

Great! I will place my order immediately (after I investigate roberta wilkinson's suggestions!)

The last few days we've had rain and much snow melt, so that my veggie beds have been revealed. There are onion greens poking up from the mulch!