Some good 'uns that I go to for various reasons include:
Maryland Flower and Foliage in White Marsh, MD, really great selection of annuals for ridiculously low prices. They don't take credit cards, though: both a blessing and a curse!
The Perennial Farm in Glen Arm, MD, is a wonderland of perennials. Go on Saturday to browse but don't plan on buying anything, the prices are so high, you'd think they fertilize the plants with liquid gold.
Poor Boy's in Parkville, MD, because after July 4 they clearance all their stock (quality stock they get from The Perennial Farm).
Behnke's Nursery in Beltsville, MD, very near my work and always has a stellar selection of everything. I usually just go there to browse because the prices are a little steep for me.
Valley View Farm in Timonium, MD, prices are a little better than Behnke's but the selection is not quite as good.
I have family that goes up to Root's Auction in Amish country, in PA. They get lots of flowers for very cheap up there. I've never been. Has anyone here gone there?