Thanks and Happy Mother's Day to you as well, I just love when all of my kids are togeher, its hard since they are 5-21 and some are away at school and have jobs, boyfriends, girlfriends etc.but we manage to pull it off every once in a while.

I hear people suggest different plants but these ones I can attest to seeing lots of bees on all the time in my own yard.
There are others but this is what I have.
Lavendar
Bee Balm
Borage
Asters
Corn flowers
Bachelors Buttons
a couple of kinds of Salvia
Anise Hyssops (agastache) this is the number one plant in my yard for bees, they just cover it and I love it too!
Russian Sage (perovskia)
Flowering herbs, they seem to be especially fond of the thyme.
Poppies
Yarrow
Catmint (but they like all kinds of mints) I just bought an apple mint for the fun of it. I am easily amused.
Sunflowers
Heathers
Ajuga
Sedum
Coneflowers
Globe Thistle
Cosmos
Clematis
Geraniums
Butterfly Weed
And of course clover and dandelions that just keep on appearing.

For trees and shrubs I have
Pear
Witch Hazel
Forsythia, they bring in basket loads of that bright yellow pollen
Flowering Quince
Mock Orange
I have other flowering trees and shrubs but I haven't noticed whether they are attracted to them.
Those would be the cherry trees and dogwoods and hydrangeas and scotch broom.I'll have to keep my eye out.
I am not sure if I missed any because I do have other types of flowers but I am not sure the bees are working them or not.
I am going to keep building up the gardens this year, not just for the bees but for me as well.
I like to have something blooming at all times so I try to find plants with different bloom times and stagger them around the yard.
I find its good to visit your local nursery once a week from spring through autumn to see what is in bloom and pick up a couple of plants each time.
Its a great way to educate yourself, at least it was for me.
Learning what blooms when and what the bees like can be overwhelming if you just sit down and try to figure it all out from a book or whatever.
When you can actually walk around and look at, feel and smell the plants, shrubs, trees and see what is blooming at the time it helps a great deal.