About a month ago all the dogwoods were flowering, and while people are very familiar with the main two Cornus florida and Cornus kousa (not native) I've never really been impressed by the attention they get by bees. These are the big flowering dogwoods with the really big white "petals" which are actually bracks, modified leaves that are white or pink colored to act like flower petals. But unlike flower petals, they're able to produce chlorophyll to a degree where as true petals and rays do not.
Other dogwoods, such as the Red Twig Dogwood, Cornus sericea, take on more of a shrub habit. They have similar flower displays to C. alternifolia but nowhere near the amount of flowers, and thus have to grow considerably larger to get the same pollinator attention.
Ptelea trifoliata. This tree has become somewhat uncommon which is a shame because bees go nuts for it. The foliage superficially resembles poison ivy, and can have a displeasing odor when disturbed. They can grow in full shade or full sun, but of course flower best in full sun. Also I've noticed that bees only work the flowers that are in full sun, often high up in the tree. (I would have gotten pictures of honeybees on this one but this isn't my tree and I didn't have a ladder accessible.) Another trait one might be on the fence about; this is the host plant to the Giant Swallowtail Butterfly, which is the largest butterfly in North America. The caterpillars mimic bird droppings and have been known to completely defoliate whole shrubs and trees of this plant! So gardeners need to choose between a good nectar plant (assuming it's in full sun) or living with flocks of the largest butterfly in North America flying through their yard.
Okay that's an ant, not a bee, but even they like to steal the nectar from some of these plants. Members of the Ribes genus are high up on the pollinator list. Red Raspberries in particular are beloved by honeybees but only when allowed to grow into a nice sized patch. Blackberries get a silver medal, maybe bronze compared to the classic Red Raspberries but are still worth growing.
Spiderwort, Tradescantia sp., these only open in the daylight hours, and are usually closed by 4:00pm. Honeybees work them, usually before noon time when the pollen is fresh. Patches of this plant need to be at least two feet around in order for honeybees to bother with them though. I planted a few dozen plants three years ago and it's taken that long for them to even take notice. Thankfully spiderwort is one of those care free natives that grows, spreads, and goes dormant with almost no maintenance or care.
Black Locust is another one that's flowering now. It's a medium sized tree with chains of white, wisteria-like flowers on it. I've been unable to find time to get pictures of it so far. The same goes for Catalpa Trees which are also flowering, and have great big white trumpets for blooms.
And a reminder that I wrote a book titled "Native Plants for Honeybees" last year on that topic. Word of warning, it's self published, and thus not on the best quality of paper. I encourage you to give the free preview a try before commuting to purchase. Reading through some of the negative reviews I see not everyone thinks my opinion on plants was worth their time, also one seemed against self published in general.