Years ago, my friend Frank Zoretich wrote a wonderful piece about that lovely smell you get in the desert when a summer thunderstorm hits. If I recall it right, the story documented Frank's unsuccessful search for an explanation.

Now comes The Wordsmith, with not only a word for it ("petrichor" - the April 2 listing if it's already off of his front page) but a possible explanation in the usage he quotes:

"Petrichor, the name for the smell of rain on dry ground, is from oils given off by vegetation, absorbed onto neighboring surfaces, and released into the air after a first rain."

Matthew Bettelheim; Nature's Laboratory; Shasta Parent (Mt Shasta, California); Jan 2002.

update: Michael Quinion has a delightful discussion of petrichor among his weird words:

The word comes from Greek petros, a stone, plus ichor, from the Greek word for the fluid that flows like blood in the veins of the gods. So the word means something like "essence of rock". Alas, it is rarely encountered.