Perennials for a Zone 6 Greenhouse

So, I'm still working on my greenhouse, but it won't be of use this spring.
I think I want some in ground perennials inside the greenhouse.
Things that bear right up to the first frost like ever bearing raspberries, or things that are zone 7 appeal the most.
I was hoping for some suggestions.

Hi William, you're gonna join the club of people in cold climates who have greenhouses? Yay!!! I love my greenhouse.

I remove the glazing on the greenhouse from April or early May till October, to prevent overheating the plants. in shoulder season I open the door or window at both ends of the greenhouse in the daytime and close them at night, and then closer to removal time, leave those open 24 hours. It's always a tricky balance between ventilating the greenhouse to prevent some things from being damaged by overheating, and protecting the tenderest things from frost.

You have zone 6 outside, right? So inside your greenhouse should be a couple zones warmer. Does it have good south-facing exposure in the winter? Mine does. My glazing is only single layer of tough UV-resistant plastic film, so it certainly goes below freezing every night during the coldest part of winter. I roughly equate the coldest part of winter with the pond hockey season here, which runs from mid or late December to early or mid February, ie about 6 weeks.

These perennials do great in my greenhouse:
Rosemary thrives in the ground in my greenhouse, but probably wouldn't survive outside. It bloomed in Feb this year, which was cute though not useful or anything.
Lots of herbs that might survive outside but have a shorter dormant season inside: oregano, thyme, mint, anise hyssop, lemon balm, chives, garlic chives. All of these were dormant in January but are greened up nicely now in mid March, and I've been using them.
Asparagus survives just fine outdoors, but produces in May outdoors. In the greenhouse it's been producing since mid February, and mostly in March.
Perennial flowers: My extravagantly big yellow chrysanthemums bloom in November to December, when everything outdoors has already died back. The iris bloom all March in the greenhouse, when bulbs outside are barely sticking a green sprout up through the mulch, and there's been nothing green outdoors for months. Calendula can be coached through the winter and keeps blooming right through though a little pathetic in the coldest part.

These leafy greens (annuals, though) love the winter in my greenhouse, and are really important to me because my region gets its road connection from warmer regions cut off for 4 - 5 months every winter, and there is no non-local fresh vegetables or fruit available in the market for all that time. So preserving vegetables and growing fresh ones in the greenhouse are very important. Eliot Coleman's books inspired me to go for lots of different winter leafies and carrots. His advice to seed them in August or September so that they are small or fully grown going into winter has worked well for me:
Kale -- I've grown others but like Red Russian the best.
Mustard greens. So many types. Mustard greens just love overwintering, and I use them in salad and cooking.
Lettuce, of course. Red varieties do a little better in mid-winter, and green varieties in shoulder season.
Arugula / rocket continues growing like a monster all winter.
Spinach and chard love the winter greenhouse.
Cilantro / coriander does fine.
Parsley can get huge in the greenhouse and sometimes I cook it like a mess-o-greens, or mix it into other greens.
Claytonia / miners lettuce: I loved it the first year I grew it but now I feel it's too little and fiddly to bother with.
Carrots: As recommended in Coleman's books I started Napoli carrots in September and they were sweet like fruits in February when no fresh fruit is available locally. This past winter I started them too late, November, and they have not sized up so I learned to start them earlier.
Beets and turnips would probably be as good as carrots and I'll try them next winter. They do great outdoors in summer here.

My greenhouse gets quite a lot of aphids in the winter, so I do a fair bit of massaging small seedlings gently, and spraying larger plants with a jet from the hose. When it warms up and the lizards and spiders get active again in March, the aphids recede. Phew!

Wow,  great feedback!
The herbs,  and the greens make so much sense.
Your seasonal isolation creates a scarcity that mimics the costs at our grocery stores.
I remember paying an outrageous cost for a few twigs of fresh rosemary at Thanksgiving.

William Bronson wrote:
Your seasonal isolation creates a scarcity that mimics the costs at our grocery stores.

Yep, and due to seasonal isolation I had already stocked up in the autumn, to last me through till mid-May. So I have little need to go to the town or stores, or newly stock up for self-isolation for the current virus crisis. I've got dry goods stocked up, spices, flour, rice, dal, pasta, veggies that I dried or pickled, salt, cooking oil, soap, etc. (Some is just my stocking up habit and wasn't at much risk of running out locally for the winter). My neighbour's cow resumed producing in early March, and my greenhouse is starting to crank out leafy greens and herbs. I only worry if I don't start rationing coffee consumption, and I just hope the electricity doesn't go out for several days at a time because I'd run out of water on day 3 or so.