Light Beer
Pacifico is as common as water in Mazatalan. For around 13 pesos, buy yourself an entire Ballena bottle. That's 1 full liter of beer for just over a buck. You can't beat that with a stick. Sol is the leading competition to Pacifico, so give that a try too.

Corona is also very common. Make sure you have some fresh-squezed limes around.

Medium Beer
Modelo Especial is by far the most common, usually sold in cans instead of bottles, this is a good middle-of-the-road beer. If Modelo isn't available, get Tecate instead. XX and Indio, are also quite tasty, but harder to find.

Dark Beer
Negra Modelo is a hearty, hoppy, full bodied beer. It's a little more expensive than the lighter beers, but if you like dark beer, this is the way to go. Also try Bohemia, if you can find it.

Tequila
No trip to Mexico can be complete without Tequila. Here in Mazatlan you can certainly drink your fill. While there are more than 30 varieties at any given liquor store, here a few of the most common: Jose Cuervo, El Jimador, and Orendain. These brands have three levels of quality - regular tequila, distilled and aged, and 100% agave. Regular tequila runs just over 100 pesos for 3 quarters of a liter. Distilled is 150, and 100% agave runs anywhere from 300 to 800. For making drinks or mixing, regular tequila is fine, but the distilled is better. You can also drink distilled Jimador and Cuervo plain, maybe with a little lime. My suggestion is - spring for the 100% agave. It's the nectar of the gods, truly. If you're really going to go for it, go for Don Julio 100% agave. This usually isn't even on the shelves - you have to ask the store owner to bring it out from in back. I won't tell you how much it costs.

Coffee Liqueurs
There are a number of coffee liqueurs available. Contrary to what you may have been told, they are not all the same. Kahlua is a little more expensive than most, but it's worth it. Don't buy anything else.

Wine
While they are not nearly as popular here as in the states, there are good wines to be had. It's best to ask your waiter what he recomends.

Other
I am sure you will be pleasently suprised with what Mazatlan has to offer. Many ipmorted liquors not available in the United States. Try Viverova vodka, it's a great smooth vodka you can't get in the states. What's best? I don't know. My advice is to try one of each.