This is one of my favorite warm-weather drinks. Although I have also been known to make them when it's cold outside, too.
Use fresh limes. It makes a big difference.
Mix together one part fresh lime juice, 1 part silver tequila, one part pomegranate juice, and half a part Cointreau or Triple Sec. Put in a shaker full of ice, shake the ever-livin bejeezus out of it, and pour into a sugar-rimmed glass.
Here's the .pdf if you want to pin it to your refrigerator so you don't forget to make one.