San Diego has a great selection of homebrew clubs, and nearly anyone should be able to find a club that suits them. Which is best for you will depend on what you are looking for and where you live. Similar discounts should be available at local shops with membership in any of these clubs.
I am actively involved in 3 of the local clubs: QUAFF, Society of Barley Engineers, and North County Homebrewers, so I can comment on these three. I don't have anything bad to say about any of them and they all serve different purposes for me.
QUAFF (meets in Mission Valley) is a huge, well-known, and long-standing club. Many of the best professional brewers in the SD area got there start in QUAFF and most are still members. Joining QUAFF is a great way to get well-connected in the SD beer community, both with homebrewers and pros. QUAFF has something on the order of 300+ members, with about 120 attending typical meetings. The guest speakers at monthly meetings are often well-respected professional brewers and sometimes bring really special beers to share. Beer sharing can be somewhat difficult with such large meetings. 2 half-gallon growlers is about the minimum to share with the entire meeting and it can be hard to get good comments with such a large group. If you bring less beer, just share with your table. The special events (holiday party, camping, oktoberfest, padres tailgate party, st pat's party, big brew day, etc) are my favorite part about QUAFF, these are a lot of fun and are an opportunity to really get to know some of the outstanding brewers in QUAFF. Even if the meetings aren't your thing, QUAFF membership might be worthwhile for the special events alone. It can be hard to get to know a large percentage of the QUAFF membership, but you will find it worthwhile if you take the time to get to know many of the members personally at events. The mailing list is very active and can be a great resource for learning, asking questions, and buying/selling equipment.
Society of Barley Engineers (meets at Stone, Escondido) is a much smaller, but well-organized club that holds formal meetings with featured topics. Because of its smaller size, the club tends to be a bit more tight-knit with most members knowing each other. Typical meeting attendance is about 35, and two 22oz bottles will make it around the room. Because less beer is required lots of beers are shared and members share their best beers. I personally share far more beers with SBE than QUAFF, because I am not usually willing to give away 2 growlers of my best beers in a single night. SBE doesn't do as many big events, but has some special meetings like beer and cheese pairings at local breweries. Most of the featured speakers are members, but a few meetings each year feature an outside guest speaker. The meetings are a much more intimate setting than QUAFF and I find it easier to pay attention to the speakers. The club also provides commercial examples of styles for most of the meetings, which makes the presentations a lot more meaningful. I'd say that in terms of monthly meetings, I probably learn the most from SBE out of all the clubs, due to the combination of the focused meeting topics, smaller and quieter setting, and useful comments on my shared homebrews. Several members are in both QUAFF and SBE, but seem to be more active with SBE (in terms of meeting attendance and beer sharing) because the meetings are smaller.
North County Homebrewers (meet at various north county locations) is a fun and casual club, and has found it's niche as being more of a social group than the other clubs that have sit-down meetings. Events are held at local breweries and at members' houses, with the location changing each month. A bar is set up for members to serve kegs at all meetings and there is almost always food, either provided by the club or potluck. There are rarely featured topics and the business portion is a quick stand-up meeting lasting about 20-30 minutes. The real value in NCHA is the opportunity to socialize and talk beer with other brewers. I find that I learn quite a bit just through the casual brewing conversations that come up. These meetings can be very valuable for getting good evaluations, because you can go around and serve your beer to people while soliciting comments, rather than passing it around the room at a sit-down meeting.
Whichever club(s) you choose, I'm sure you won't regret joining the great homebrew community and getting to know more brewers in the area. All of the clubs are glad to have prospective members come by for a meeting or two without officially joining, so you can certainly try them all out before you decide.
