I am going to have to nix Hopping pig. I've been there three times and their servers are just really really ignorant about beer, and their pours are stingy. There are so many great craft beer bars in SD County there's no need to go to a mediocre one. The Tipsy Crow is the spot in the Gaslamp, and if you can get about 5 minutes north on the freeway hit up the Blind Lady, Small Bar, Tiger!Tiger!, or Hamiltons. Most restaurants downtown pour SD Beer. If you have transportation, Stone Liberty Station is pretty sweet, and I would suggest getting up to the Miramar/Mira Mesa area where you have a ton of choice for breweries, and it's not as far as the Vista/North County contingent. There you'll find:
Green Flash
Hess
Wet 'n Reckless (you can skip this one)
Ballast Point
White Labs
Intergalactic
Alesmith
Rough Draft
Modern Times
St. Archer
and a Karl Strauss brewpub that has great food and a nice view.
A little further south you have Societe and Helms too, which are fun.
Have fun! It's a great place to be for Craft Beer no matter where you end up.