lots and lots of things a few examples are;

OxTail Daisies
QueenAnnes Lace
butterflyweed
virginia creeper
purple loosestrife
jewelweed
ditch lilies

there are plenty of cultivated plants that are more 'weedy' than these.

there are a lot of very useful herb weeds, not the latest and greatest hybrid cultivars, but the old pull your hair out trying to get rid of weeds, some with their names right on the chemical bag, some of my favs.....
dandelion
chicory
plantain
chickweed
elecampane
mullein
comfrey
yarrow
purslane

Since I love natives, many things in my yard would be considered weeds by gardening "experts." I take care of a native section in a public garden, and we have an aster that, when it blooms, is an incredible dark purple. However, prior to blooming, it really does look like a weed! I have yet to key it out successfully. We got it on a rescue. Also, I have many carexes that are becoming somewhat popular now in the trade. C. plantaginea or seersucker sedge is one of my favorites. A shade plant, it normally grows in damp conditions, but at my house it is in dry shade and never misses a beat...even this year! It is evergreen here in zone 7. Fraiser's sedge is good, too. Of course, my favorites are Trilliums and Hexastylis, evergreen gingers, but nobody calls them weeds! Oh, when I made five years with Master Gardeners, they gifted me with a weed book. I immediately told them how many of these weeds are great for gardens. Example: Joe Pye is now a garden favorite. Now, if I could just get rid of the Japanese stilt grass (Microstegium vimineum) I would be happy.