The Plants Database at Dave's Garden nice big type, very nice thumbnails and large photos. Not as extensive listings as above two but there is an Identification Forum where you can post a photo of the plant you are trying to identify.
Wildflower Database at MyWildflowers.com a database of wildflowers, with photos. Users can search for a flower by name, family, or other criteria. The site also include a unique identification tool that allows you to enter a few features of a flower you've seen (like color, height, leaf type, shape, etc.), and retrieve a list of flowers that match those criteria.
|The Botanical Garden Volume II - Annuals and Perennials -
Roger Phillips, Martyn Rix - 2002
Over 4,000 color photos of leaves, bracts, blossoms, rhizomes, and root structures with scientific names, description, locale and cultivation information. Text is scientific. Common names not given for many of the plants.
more info: The Botanical Garden: Perennials and...
|Botanical Illustration in Watercolor - Eleanor B. Wunderlich -
more info: Botanical Illustration in Watercolor
|The Botany Coloring Book - Paul G. Young, Jacquelyn
Giuffre (Illustrator) - 1982
more info: The Botany Coloring Book
|Identifying and Harvesting Edible and Medicinal Plants in
Wild (And Not So Wild Places) - Steve Brill, Evelyn Dean -
more info: USA: Identifying and Harvesting Edible and...
|How to Draw Plants : The Techniques of Botanical
Illustration - Keith R. West - 1996
more info: How to Draw Plants : The Techniques of...
|Just Weeds : History,
Myths, and Uses -
Pamela Jones - 1991
nice, large color illustrations, interesting and helpful text
Book, 2001 Edition - Kathleen Norris Brenzel -
more info: USA: Western Garden Book, 2001 Edition
Europe: Western Garden Book
Although this book is written specifically for the western US, the information is helpful worldwide