Tempus on tap. Cosaco produces an Amber Ale (la guera), a Red Ale (la roja), and a porter (la oscura). Personally, I think Cosaco beers are very mediocre, although certainly better than a Corona. If I have to drink Cosaco, I'll drink the guera, and the porter is passable. Stay away from the roja at all costs. For Tempus, they have the clasica and the doble malta. All Tempus beers are very malty, and the doble malta is a pretty decent beer with strong malt and caramel flavors. The clasica (or dorada? I'm not sure) is pretty bad though, almost sour, I do not recommend it. If you happen to be with someone else with bad taste in beer, they also have one of the major beer brands on tap, I think Sol but I could be wrong. It doesn't really matter what it is though, trying to differentiate among the variations of clara or oscura of any major brand of Mexican beer is a near impossible task.
Calavera and Azteca on tap, though they often run out and the particular styles they have change often. I highly recommend trying whatever they have by either of these breweries. On my last visit, I sampled the Azteca Manzana Ale and the Imperial Stout, both excellent beers. On the menu, they also list a stout by the Beer Factory, but they have never had this available on my many visits to Zazá within the last year. All the microbrews on draft cost 55 pesos.
Not only is this a great place to drink, Zazá also makes pretty incredible brick oven pizzas. One of the biggest problems with most pizzas in the city is the crust, but Zazá gets the crust just right. Their medium pizzas run about 100-140 pesos and are probably enough for two people, unless you are like me and can eat an entire pizza no matter what size it is. They also have other appetizers and entrees, but I haven't had anything else there except the french fries. If you are looking for a slightly more upscale place to eat before or after having drinks at Zazá, you can also check out Casa D'Italia and Vecchio Forno, which are just a couple blocks from Zazá.
As far as the atmosphere goes, Zazá is extremely laid back and informal, which is just the kind of place I like. They usually have music playing, but it is never too loud like a lot of establishments, and it is usually an eclectic of mix of jazz, garage rock, classic rock, soul, ska, and punk. My only gripe is that while the music they play is usually pretty good, it just sounds like someone put their ipod on shuffle, somewhat ruining the ambience of the place. The staff is fairly friendly, although usually completely unknowledgeable about the beer. Make sure you ask several times what beers they have until they actually go check. Since Zazá is pretty far out of the way compared to most other places in Condesa, there isn't much else around and fortunately this means there are very few ambulantes passing by annoying the customers.
Zazá is located at Pachuca 1, right on the corner of Pachuca and Veracruz, just a few blocks from the Chapultepec Metro stop.