I grow both native and Spanish bluebells (separately so they don't interbreed), perenial cornflower, nigella, several different types of campanulas, dark blue salvias, myosotis (forget-me-nots), polemonium (Jacobs ladder), larkspur, viola and dogs tooth violets, scilla, crocus, muscari, chinodoxa, irises, dark blue aquilega, linaria (toadflax), primula, asters, geraniums particularly Johnson's Blue, aubrieta, Delft Blue hyacinths, ceanothus, lilac, lavender, rosemary, hysop, fuscia, passion fruit. There are also hebes, buddlea, heliotrope, ipomoea, agapanthus, alliums, anchusa, sweet peas, chicory, gentians, pasque flower, tradescantia, delphiniums, lupins, limonium, scabacious, heathers, ageratum, nemophila, lobelia, petunia, streptocarpus, annual cornflower, linum (flax), verbena, eryngiums, vipers bugloss, that I have grown in the past. Then there are plants which I haven't grown such as several types of blue clematis, wisteria, hydrangers and blue leaved plants such as some pines and the rose Blue Moon. I could go on! It is difficult to single out a favourite, they all have their place.