Interesting you should ask. Most people don't give a damn and you'd be surprised the number of people who use iodized table salt for everything.
I'd say 90% of my "regular" cooking is done with either Kosher salt or a variety of sea salt. Unless it's a specific kind of "cooking" where I need something special such as pickling, curing, certain Japanese cooking, etc...
For Kosher salts, the two most commonly found brands in supermarkets are Diamond and Morton. Of the two, I prefer Diamond for it's bigger crystals and airier, smoother flavor.
When you go into sea salts, there's an infinite number of brands and kinds and it really becomes specialized to a degree. I prefer ones that have a more complex mineral flavor.
Lastly, I like using finishing salts, whether it be smoked salts, fleur de sel, sel gris, etc... A lot of foods, whether it be meats, seafood, fish, vegetables, etc.., can be taken to the next level just by sprinkling a little bit of finishing salt at the very end right before or during plating.
Salt is without question the most important seasoning agent in cooking. I'm of the mindset that when you salt foods, it should be salted in stages during the cooking to develop and build layers of flavors.
For example, almost every recipe will lay out ingredients by volume or weight and the procedure will always just say "add salt and pepper to taste" or just give a measurement of 1 tablespoon of salt and will tell you "add salt" in the procedures. When in fact, you should be salting the onions, celery and carrots as they are sautéing so that they taste good and by adding salt you bring out their natural flavors. Then as you add something else, you season again with salt and so on. By salting each component in stages, each ingredient's flavor gets maximized by the heat, salt and other seasonings, and this is what chefs mean when they say "building layers of flavor".
Take a look at these two sites as well for online purchasing:
http://www.artisansalt.com
http://www.atthemeadow.com/shop/
trhee I am curious what kind of salt do you use in your cooking. I enjoy watching cooking shows and occastionally I will see a particular type of salt, usually sea salt used, so I go the Saltworks to get some to try, real cheap and fun reading up on the history of a particular salt. My current favoritre is Bali Pyramid Sea Salt. The only one, so far, that I don't care for is Peruvian Pink Salt is has a metallic taste to it. I use it to boil pasta in.