This is my first post; I couldn't resist, I live here.
English Ales in Marina (about 10 minutes north of Monterey) is my local haunt. A nice brew pub. Mostly English styles. The IPA is my favorite right now (an English style, though, not a hop bomb) but my favorite changes every few months. It is where I go to watch Giants games.
http://www.englishalesbrewery.com/
A new place just opened on Cannery Row called Cannery Row Brewing Company. I sort of have mixed feelings about it. It is overpriced and caters to tourists, but they have around 70 beers on tap. Some good (off the top of my head: Stone IPA, Arrogant Bastard, Anderson Valley Summer Solstice, Affligem White, Racer 5, Green Flash IPA, some Belgians, a bunch of others) but I question their judgment on many of their selections. Also, they don't brew anything, they just jumped on the "call ourselves a brewery" bandwagon. I think Lagunitas makes a couple of their "house" brews, though.
Previous poster mentioned Crown and Anchor. They have Young's Double Chocolate Stout on tap. For me that alone makes it worth visiting.
Also downtown is Peter B's. They have some nice brews as well. I usually get the Pilsner. Be forewarned, though, they have a Dark Wheat on the menu, but what they do is mix their hefe with their stout. That pissed me off the first time I ordered it. Also, it is attached to a hotel, so the atmosphere is a little sterile.
If you make it out to Salinas (about 25 minutes East of Monterey), there is Monterey Brewing company. It is over by the Steinbeck center in downtown Salinas. They have some pretty good beers and a decent restaurant. Last time I was there ( a couple of weeks ago) they had a great cherry wheat summer seasonal. Not cloying at all, just a crisp American style wheat beer with a hint of cherry flavor. I really like their Pale Ale also.
If you make it up to San Francisco, I would recommend going to Rogue Ales. It is their only outpost in California and well worth a visit. Last time I was there they had like 16 Rogue beers on tap (plus a bunch of visitors). It is over near North Beach (I think on the corner of Powell and Columbus) There is a bar specializing in Belgians right down the road from Rogue. They have a good selection, but it is super yuppie and expensive. It is called La Trappe and is like a block down Columbus from Rogue. Also, for a great snack, there is a little sausage diner type place called Show Dogs. It is on Market and they have great sausages and about 8 beers on tap, usually a good selection.
Also, I don't know if you are a baseball fan, but 21st Amendment Brewery is walking distance from AT&T park ( where the Giants play).
If you head over to Berkeley, be sure to check out Triple Rock (on Shattuck).
If you do head up to Santa Rosa, (well worth the trip, BTW, the Russian River pub is amazing) you should also check out Bear Republic in Healdsburg, about 15 or 20 minutes north.
Hope this helps. Enjoy your stay in Monterey.
Heath