Olive oil is an essential addition to anyone's kitchen. Olive oil is different from any other oil in that it is essentially the fresh squeezed juice of an olive, with no chemical processing at all. Nearly all seed oils (canola, soy, vegetable, corn, etc) are heavily refined and offer little health benefits and if you ask me, are doing you more harm than good.
Olive oil is high in polyphenols (a type of vitamin E), which is a powerful antioxidant that is only found in olive oil as opposed to any other oil, and is high in healthy, natural Omega 3s. Of course, to gain the most benefits from your olive oil, it is important buy a high quality Extra Virgin Olive Oil. I began learning about olive oil a few years ago during a trip to Italy. I was astounded at the difference between a good quality oil and the standard popular supermarket oils like Bertoli and Filippo Berio I had been buying for years. A high-quality EVOO should be complex in flavors (anywhere from grass, almond, artichoke, to apple) and be slightly bitter and pungent. Essentially, the more bitter and pungent (think of a slight tingling sensation in the back of your throat) an oil, the higher it is in polyphenols and the healthier it is for you.
Also, it is a common myth that you cannot cook with olive oil. Throughout the Mediterranean they have been cooking with it for centuries, and they're some of the healthiest people on the planet. I've even fried french fries in EVOO like I ate in Italy and they're delicious! The key is to heat the oil just below its smoking point (450 degrees F). Olive oil is the only oil I have in my kitchen and I use it for everything from baking to frying, and of course, on salads, as a finishing oil or just eating it plain with a slice of fresh baked bread.
Some supermarkets are beginning to carry more higher-quality oils. Look for an oil that clearly states where the oil comes from, or displays a certificate of origin symbol (PDO, PGI, DOP, IGP) to ensure the oil does in fact come from that particular region, however there is no guarantee how fresh the oil is, or how long it has been sitting on the shelf as light is the biggest killer of a good olive oil. I find the web is the best place to buy quality oils as they seem to be imported from people who know a lot about olive oil. I've ordered from olio2go.com, deandeluca.com and oliveoillovers.com who has a good collection from people like Castillo de Canena, Frantoio Franci, Terra Creta and Oro Bailen (my favorite!).
I also agree with another user who mentioned the book "Extra Virginity" by Tom Mueller. I learned a great deal from that book and it was quite the eye opener.
Hope I've convinced you to love oil oil as much as I do!