Squashes, pumpkins, gourds, and garden cucumbers stand out as needing and feeding native bees, as do melons, even the seedless varieties. I also let my arugula, mustard and other early salad greens in the cabbage family go to flower (collecting the seed for future planting). Bumblebees at least will work your tomato flowers for pollen, although outdoors, many varieties of tomato do not benefit much from their pollination. Alas, peas and beans (except fava) self-pollinate in the bud. More inviting vegetable garden flowers for bees are to be found among your herbs, such as dill, lavender, rosemary, oregano, mint and chives. With bees and beauty in mind, I also slip attractive flowering species amid my rows in the vegetable garden. Sunflowers or their kin are nice for this, just avoid the weird horticultural creations that lack pollen or have doubled or ruffled flowers.
-Jim Cane, USDA-ARS and Utah State Univ.