Freshly ground coffee has more flavor. Coffee grinders come with the high-end conical burrs, flat burrs or a cheap metal blade.
Grind your coffee -- it will have more flavor. Different processes of extraction requires different grind, but every one I'm familiar with is finer then the grinder in the store will produce. The pre-ground coffee quickly loses its flavor, and the preparation of your own cup loses part of its mind-clearing choreography.
The coarsest grind used for French press, finer one for the drip machine, finer one for espresso, and still finer for the Turkish coffee, which I like best. With steel blade coffee grinder you can effect the grind by different grinding time. Burr grinders are set to desired coarseness.
Burr grinders (also called mills) can be electric or manual. Electric ones are obviously faster, while manual with comparable burrs are cheaper. Zassenhaus with adjustable steel burr mechanism and beautiful traditional wood and copper exterior cost $66.
Electric burr grinders are heavy and stable. They have a top chamber called hopper to put the beans in, and the lower one called coffee bin. The burrs are in between. Conical burrs mill the beans slower and cooler than flat ones, but flat burrs last longer. Cool milling matters, because heating by friction is still heating and it cooks the beans.
I have to turn the burrs in my Solis conical burr grinder to set the particle size (there is a dial marked from French press to Turkish). I hold the "on" button or set the timer to get the desirable amount of coffee.
Burr mills cost anything between $50 for Cusinart Supreme Grind to more than $1500 for heavy-duty commercial pieces. Solis costs $150. Burr mills seem to be well and thoughtfully designed mechanisms. Different price reflect their durability and size -- you get what you pay for, at least within the reasonable range.
Steel blade grinders are cylindrical, with electrical motor inside the body and the small chamber with the blade on top. They have a cross-shaped blade like one in a food processor. Coffee beans go in the chamber, the transparent plastic lid goes on top, and you regulate the grind by holding down the button in the lid. Watch for the powder spillage when you open the machine. To get coffee out of the grinder, scoop it out with the tea spoon. Or turn the grinder upside-down.
Blade grinders are cheapest on the market, starting at $9 for a Hamilton-Beach Proctor Silex. The principal drawback of steel blade coffee grinders is that it results in particles of uneven size. The extraction of oils and caffeine depends on exposed surface of the particle. Turkish coffee can be forgiving: if you have enough of the fine powder, the coarser particles will eventually settle in the mud. You just throw away some coffee, that's it. Espresso from the uneven grind will be either too bitter or weak and flat. Beside this major problem, since blade grinders are low-end, they often have some ill-designed features. That include aforementioned spillage, too short or too long but not flexible cord, button breaking off and ground coffee getting into the electrical system and clogging everything. There is no obvious way to clean the blade grinder. When my was getting clogged, I used to fiddle with a toothbrush or a wooden toothpick. Since I bought my Solis conical burr grinder at Sweet Maria's, I use the old whirley blade for poppyseed.
See also: kitchen, turkish coffee.