Dandelion is the common name for Taraxacum officinale, a genus of flowering plants native to Europe, North America and Asia. The English dandelion is a corruption of the French dante de lion which translates to "lion's tooth," a refference to the deeply serrated leaves of the plant.
The flower head (floret) of the dandelion is actually several small flowers grouped together. You may remember Dandelion Wine by Ray Bradbury from your summer reading lists when you were a kid. In the story, the wine made from dandelion petals is a metaphor for capturing and bottling the joys we experience in summer. Gardeners and landscapers who like manicured gardens and lawns may not get all warm and fuzzy over the dandelion connection to summer. The taproot of the dandelion can make pulling them out difficult and the dispersal of dandelion seeds basically assures that some will find their way into your garden.
If you change the way you think about dandelions (and many other "weeds") you'll start to see them as more than a nuisance in your garden. In the early spring the flowers are an important pollen source for bees. The aforementioned petals are used to make dandelion wine, the leaves too can be eaten by people. Dandelion greens are a little bitter but are an excellent spring crop rich in vitamins that can be added to salads or stir fries.
Since the Middle Ages the dandelion has been grown as a food crop and for medicinal uses. In today's vitamin stores you may find products made from or containing parts of the dandelion being sold for its diuretic properties.
Recently, I was pointing out a tulip to my nephew (who is four years old) when he said: "Oh yeaaaaaah, and those are called wishes," pointing to the first dandelion of the season. I swear I almost lost it. If the wine, bees and dandelion greens aren't enough reason to pardon the dandelions in your garden then consider the kids in your life. How can you kill a wish?