Question
There's got to be some way of identifying most flowering plants without the flowers. I mean, I can tell a dandelion leaf just by looking at it, so why shouldn't I be able to do that for most other plants? Yet I can't find ANY wildflower guide that allows you to identify plants by their leaves. Do you know of any flower guide that tells you this stuff? Is there some way to go about doing it using a regular flower guide?

Answer
you have to look past the flowers to see the leaves.
regular flower guide ID books(good ones) show the leaf of the flowering plant also. through practice you can learn to ID many flowering plants by their leaves. look at them while they have flowers on them and see what type leaves they have. plants are classified and named into groups by the type of flower they have not leaves.  trees, shrubs, herbacious plants, perennials, biennials, annuals are all classified this way. except for spore producing plants(ferns, etc.) all plants produce flowers as a reproductive organ. a begonia is a begonia(angel wing, rigor, wax, etc.) because they have the same basic flower structure. the leaf structure on them varies widely (small oval to big angel wing). this is true of many(thousands) flowering plants.
get to a barnes & noble or other bookstore and look for the best wild flower book you can find that shows leaves also. i sold flowering plants(annuals, perennials, houseplants, etc.) for 20+ years and learned to ID them from there leaves when they would come in during the beginning of the season before they had flowers on them. i know it's the old fashion way, but what else can i say. visit a local garden center/mass merchandiser and look at all the flowers they sell and note the leaves that are on the plants also.
good luck
sorry there isn't an easier way
rick