1) Your irises are absolutely lovely. That is what they are supposed to look like. Gorgeous.

2&3) Definitely a weed, though the name is escaping me right now. Since they are so big and tall, hand pulling is your best bet.

4) Also a weed. Could probably be taken care of with some round up.

9) Looks like a hydrangea. Are the blue flowers - do they kinda look like big blue snow balls? If so - that is hydrangea. The color can change due to acidity of the soil.

11. I'm not sure what it is, but it has shown up in my shade garden on it's own. It's been there for 2 years now and hasn't flowered. But I like the visual interest, so I leave it.

12. Looks like some type of apple/crabapple volunteer. Does it make any small fruits in the fall? Though it may still be too young to.

7/8) looks like lilac

10. leucothoe
    11)euonymus, maybe 'emerald gaiety'?
11. looks like bishop's weed, aegopodium. this one is actually sold in garden center's though so don't let the name fool you. it is a spreader and gets queen anne's lace-like flowers

These threads are so fun for a plant nerd like me!

2&3 Curly dock, a weed with a tap root, so dig out with a tool that is narrow and deep like a dandelion digger.
4 sorrel, a weed with fine underground runners. Have to weed often and as completely as possible to get rid of it as it resprouts from roots that break off or Roundup works on it relatively well. Pull before it goes to seed (tall stalks currently on it are either blooms or seeds)
5 False Solomon's seal (Smilacina racemosa), a nice wildflower. Will slowly increase if you let the berries develop.
6 I'd guess a weed (but not sure) since I have a weed that comes up in my garden that looks similar
7 & 8 Lilac - should have scent
9 Hydrangea probably
10 Leucothoe

11. Euonymous- keep an eye on it and prune where you don't want it as it will spread, but not rapidly
    12 Gout weed or Bishop's weed (Aegopodium)- will spread and is hard to remove since will sprout from any little root. If not contained I would consider taking Round-up to it before it gets totally out of hand (though you will have to keep the Roundup off other plants as it will kill them also)
    13 Apple most probably or crabapple
    14 Musclewood AKA Amaerican hornbeam (Carpinus caroliniana) Nice small native tree
    15 Not sure, but if a pair leaves come off exactly opposite each other on the stem, it's a native viburnum, but I can't remember which off the top of my head

4 - sorrel is a weed? It's so much better than spinach. We grow it at the end of the garden and make sorrel borsch out of it. Eat it raw as well... has a kind of sour taste.

There is garden sorrel with large leaves and wild sorrel AKA sheep sorrel with tiny leaves and a serious habit of spreading by underground runners and seed. They may or may not be related (the wild one is Rumex acetosella) but they aren't the same plant at all!

#6 - One of the Avens? Geum sp.