Most annuals still have time to bloom. For low maintenance look for native to your area, and profuse seeding so they reseed themselves in your plot. You could still get Sunflowers planted at this point and get blooms for fall is you choose especially short season varities - some are only 50-55 days. Yes, still time for Borage. Another annual you could plant now would be bachelor buttons. Also, poppies.
Perinnials you could still hope to see flowers from -- black eyes susans, blanketflower, milkweed, any and all in the mint family including bee balm (also called bergamont), and maybe anything in the salvia (sage) family.
Happy planting!