The 3rd one is Coreopsis. 1st one is a weed.

Seriously?! Sure about that? Do you know what it's called? If not...how do you know it's a weed? I originally thought it was a survivor from last year's "wildflower mix" which produced all kinds of weird stuff.

Do gardeners ever allow "weeds" in their gardens or is that a bad idea? I thought the lemon-yellow color of this plant was a perfect offset to all the orange-yellow coreopsis and stella d'oro daylilies. I was very glad it had invited itself into my garden to fill up some empty spaces and give me some interesting color. If it's a weed, I wonder if it will come back next year!

The lemon yellow flower is evening primrose, some think of it as a weed, some think of it as a wildflower. I let it grow here and there since it does look nice and I like the height, but it's like you said, more of a filler until something better comes in. It will die after setting seed, it will set a ton of seed btw.....

Thanks for your info, Kato! I don't know where it came from unless it was in the 'wildflower mix' I planted in april 2011. And it waited a year to come up!

So, about 'setting seed"...that happens after the flower drops off? So if I pull off the flowers, will it live longer?
Will it come up next year? I thought I saw it being described as a biennial somewhere. So after 2 years, it's history?

When the blooms droop and fall off, the little stub that remains will become the seed pod. Picking these off might make it bloom a little longer but I never tried it.
It probably did come in your wildflower mix, or the seeds just blew in. Last summer it would have made a leafy clump, this year it produced a bloom stalk and is in the process of blooming itself to death :(
But there will be kids I'm sure!