Many people think that vodka is made from potatoes or grain, but the truth is that vodka can be made from any source material. Traditional sources tend to be potatoes, barley, and wheat, but other sources can be (and sometimes are) things like rye, sweet potatoes, cane/molasses, beets, and fruits like grapes and apples.
What defines vodka is this: whatever fermented source mash present is distilled to a high enough percentage alcohol (removing enough impurities) in order to achieve a clean, subtle flavor. Put another way: vodka's lack of flavor is (traditionally) what defines it. The process to make vodka removes so much flavor that it doesn't matter whether you begin with grape juice, malt wort, or molasses.
Many new age vodkas go about distilling more lightly in order to keep natural flavors, but the vast majority of traditional vodkas aim to eliminate flavor, not keep it. This is why it's recognized that the many vodkas' flavor comes most from the water used to dilute the distillate.
Does this mean that vodka has no value and should never be used in drinks? Not exactly.
Vodka has the ability to enhance the flavors of simple cocktails, and sometimes even alter them a bit to something that's a bit greater than the sum of its parts. And, depending on the vodka, you can also occasionally pick up some of the vodka's own characteristics in a drink.
As for vodka brands, there are a few widely acclaimed ones to which you should probably pay attention. Tito's Handmade vodka is one that comes to mind.
Another brand which is gaining popularity is Iceberg vodka, from Canada. The water for this vodka is acquired by the harvesting of icebergs that break off from Greenland and float to Newfoundland at a place called Iceberg Alley. Gimmick or not, the vodka is good. Its sweet on the tongue, and I can detect hints of citrus in it. This bottle was sent to me as a sample, but any follower of this site knows that I don't hesitate to point out faults with freebies, if any. I would recommend Iceberg to anyone.
Three drinks come to my mind when I think of tasty vodka cocktails.
The first is simply a Vodka Gimlet. You can read about the Gimlet here and my rant about Rose's Lime Juice here.
The second is the simple Vodka Cranberry, my favorite version of which is below, along with the legendary Moscow Mule.
1.5 oz vodka
4 oz cranberry cocktail*
1 wedge lime
Combine vodka and juice into a glass, squeeze lime wedge into glass and then toss it into the mixture. Add ice, and stir.
*Cranberry cocktail, the kind that has a plethora of other juices to sweeten it. If you try to go new age and use a fresh squeezed organic not-from-concentrate cranberry juice, the cocktail will be undrinkable.
2 oz vodka
1 oz lime juice
3-4 oz ginger beer
Build ingredients over ice and stir.