Aggressive? It does not seem so at our land. Our open land is about an acre and our neighbor keep a 3 acres land open. And this is the open patch of Coreopsis I've seen. The entire 4 acre land is dominated by goldenrod, milkweed, sulfur cinquefoil and Mugwort. Even black-eyed Susan sends far more plants than this plant. Coreopsis sends beautiful flowers. Also, since this is open land, I'd rather want to have more wounderful wildflower.

Definitely a species of Camassia aka Camas or "Wild Hyacinth" (the colloquial common name in the PNW). A mid-late spring bloomer, depending upon species to about 12 to 18 inches. Pretty hardy and trouble free. Bulbs are widely available from the major mail order bulb houses like Brent & Becky's, Van Engelen, McClure & Zimmerman and generally pretty cheap. Here is a link that might be useful: Google Image Search Results for Camas

Kalanchoe. Asked about repeatedly on internet gardening forums. Congratulations on getting it to bloom.

Okay, I think it's a potentilla. Found it in a weird way...couldn't see the leaves clearly, so googled "5 yellow heart-shaped petals" and found this picture: http://www.flickr.com/photos/beakers_glass/2289307770/in/photostream/ Since the parts I could see seemed to match, I looked for those leaves in your pics and I see them (or at least something similar). That I recognize as a possible potentilla leaf. So google "potentilla usda" and see that there are 84 species in the U.S. Go through the maps and see which ones are in the NJ area, and see if any match. Probably by the time I've done that, someone else will come along and already name it! Here is a link that might be useful: Potentilla species