According to New Scientist, a good wine glass can really enhance the enjoyment of wine. Drinking it out of a plastic cup or a mug is a very different experience than drinking it from a wine glass. Try it; you'll see what we mean.
A wine glass should have a tulip shape (narrow at the top and wider at the bottom) and a long stem. The shape helps bring out the aromas in the wine. The stem allows you to hold and swirl the wine and release the wine's bouquet without heating the wine with your hand, which can bring out too much alcohol flavor.
There are dozens of shapes of wine glasses that correspond to each kind of wine. Don't bother buying them all. A Bordeaux or Burgundy sized glass can be used for both your white and red wines. If you want to expand your collection a little more, the next step would be a smaller glass especially for white wines, such as those made for Chardonnay or Sauvignon Blanc. Finally, you might want to step up to a cordial glass for port of desert wine.
Riedel is the current authority on Wine glasses, although Spiegelau and Ravenscroft are quickly nipping at Riedel's heels with quality stemware at a fraction of the price. We just found a six-pack of Spiegelau Bordeaux glasses for only $55.