Plants.am brings you a wiki encyclopedia of plants, with photos and discussion forums.
Lists: garden plants, common houseplants, fruits, vegetables, plants (by common name), trees, shrubs (bushes), edible seeds, edible nuts, herbs and spices
Categories
Growth habit - Vine (Climber), Tree, Bush (Shrub), Groundcover
Edible - Fruit, Vegetable, Herb, Nut
Lifespan - Annual, Perennial, Biennial
Exposure - Full sun, Part sun, Shade
Hardiness - Hardy, Half-hardy, Tender
Miscellaneous Categories: Deciduous, Evergreen, Pond (Water), Flowering (only if flowers are notable), Scented (either flowers or foliage), Bulbous (incl. Bulbs and Rhizomes)