Before I discuss specific plants, please be diligent in your research before you eat them! I am no expert and you shouldn't entirely trust me on what you should and shouldn't eat. These first few are relatively straightforward, but many others have poisonous look alikes.
Also, watch where you're foraging from. Keep away from roadways where pollutants can settle on your snack. The Wildman suggests a minimum of 50 feet away from roads. You should also avoid areas that may be sprayed with pesticides.
Our community garden plot is infested with mint. This makes foraging for mint very easy. You can identify it by the minty smell. It can really overwhelm some parks and garden areas, so you should definitely explore and try to find a mint patch! Several of the other plots are infested and I like to walk in between some of the plots and collect the huge amounts of "border mint." I've found a few varieties, but prefer the spearmint (or what I think is spearmint) which is darker and more flavorful. I toss a fistful in bowling water and make delightful mint tea. When the lemongrass starts to grow, I'll chop that up and add it for lemony goodness. You can hang the mint upside down to dry it out and use when the fresh stuff is gone.
Dill also likes to invade our garden. It's identifiable by the dilly smell when you crush it between your fingers. It looks like a small carrot top and tries to pass itself off as a carrot sometimes. However, it smells much better than carrot greens! One of the garden plots has not been used and is covered in dill. I have decided to ignore the possibility that the would-be gardener actually decided to grow a dill patch and have been collecting my dill there. I especially like covering asparagus with olive oil, dill, and salt and roasting it in the oven for 15-20 minutes. You're supposed to store dill in a jar of water covered in a plastic bag. That seems to working alright so far. I haven't experimented with drying it, but I presume it's similar to mint.
For weeks and weeks, I've been obsessed with positively identifying lamb's quarters. It's a green similar to spinach and I heard it was quite tasty. However, I kept getting nervous that I was not correctly identifying it. The several sources on lamb's quarters showed varying types of leaves and made me uneasy about what I'd been finding, although I had a strong feeling that I had it right. I've compared it to many sources many times and have now decided I know my lamb's quarters. The leaves are diamond shaped, with the base of the leaf fatter than the end. The leaf edges are notched and the stems have grooves. The younger leaves are covered in a white, powdery substance. There aren't any poisonous look-alikes, but some relatives aren't that delicious and can be mildly irritating.
My lamb's quarters experience taught me that you can read all of the guides, but until you've actually seen and connected with the plant, you can really second-guess yourself. It really helps if you have someone show you the plant live. (Thanks to Eric for connecting me with purslane! I'll chat about it when I see more pop up!)
You can use lamb's quarters like any other green. I stir-fried it up with a touch of oil, lots of pepper, and soy sauce. The leaves shrink by about two-thirds, so make sure to keep that in mind when you're cooking! I underestimated its amazing shrinking abilities and ended up with a very peppery dish. You can mix it in with other greens if you want to slowly introduce it to your taste buds, but eating it by itself will allow you to full acknowledge its deliciousness.
Hemlock
This is not edible and is actually very poisonous. Susan thought it looked pretty and picked it up to put in our awesome chemistry themed vase. I wasn't sure if it was Queen Anne's Lace/Wild Carrot or Hemlock. After consulting with the Wildman's book and the internets, I'm going with hemlock. Not like we were planning on eating it anyway. Until you're a pro, stick with the easily identifiable plants that don't have highly poisonous dopplegangers.
Foraging can be a lot of fun, so I encourage everyone to partake at what ever level they feel comfortable with. It's delicious, introduces you to new foods, cheap, and has a low environmental impact.
And if you really can't find any mint, dill, or lamb's quarters, Susan invites you to help weed our garden!