Geosmin smells of earth:
You can smell vanishingly small amounts of it, too - mere nanograms of the stuff! It smells this way for a reason - countless soil bacteria busily produce it in your backyard as you read this.
The first thing I thought of when I started this entry was Demeter's Dirt fragrance. I imagine this has to have some of the stuff in it - I've only ever smelled it briefly in Whole Foods, though.
I love smell because I never fail to marvel at the fact that a pure single molecule can exhibit such complex aromas. My favorite example is acetophenone.
I also love smelly molecules. It is one of the things that attracted me to organic chemistry in the first place. In fact, our lab just got aldrich's flavor and fragrance catalog in today. I only ordered it because it'd be fun to flip through.
I wish I had a reason to order some geosmin. =)
It's also REALLY hard to get rid of (because of its generally extremely low concentrations). It's a fairly common problem in drinking water treatment -- people don't like their drinking water to smell like dirt, so we often have to design in GAC adsorbers or ozone/h2o2/fenton's kinda stuff to get rid of geosmin and 2-mib.
One word: petrichor. Although I think they found that that was made of ~40 different scent molecules.
A big winner is [E,E]-farnesaldehyde, Lily of the Valley. The nitrile is similar and more stable. The scent is counterfeited with bourgeonal.
(-)-[4S,4aS,8aR]-Geosmin is the bane of water districts. With a sensory threshold of 0.1 ng/kg tap water complaints flood in with just a teeny contamination.