Patuxent Nursery occasionally has really good deals on some plants. In the spring, they have a great deal on impatiens and other summer flowering plants - I think it was $1.25 for a pack of 6 small plants. This can make things confusing later, though. I went back a couple months later and thought I found another great deal - 18 plants for only a couple of dollars. I was wrong. Read the fine print on the signs before buying. I ended up returning to the shelves a whole tray of beautiful plants.
They also have a good variety of stones and pavers for landscaping.