College Billiards and On Cue billiards in La Mesa are known as being the main players rooms. There is a pool hall out east in El Cajon where some players are who like to gamble; this hall is next to a store that makes the Dead Stroke shirts.
You won't find too many serious gamblers though. Ask for Sam Manoale or Vic Castro at College (Vic was a former pro on the camel tour and plays one pocket). If you go to a tourney night at On Cue or College you'll see most of the players who gamble in the city.
They used to have a lot of golf games on the snooker table at College but sometimes the latinos gang up and sell out to each other ( I call it the "torta" maneuver) and people stop playing.
College billiards is in a bit of a shady area so you need some city sense; the last time I was there my friend ran up and said some guy just stole his new motorcycle from across the street from the pool hall. It's a little ghetto-ish but not too bad usually; watch yourself at night.
If you are in SD on a Sunday, call Gaslamp Billiards and see if there doing their $5 special. This allows you to play all night on Gold Crowns with good cloth in a upscale atmosphere downtown. Food sucks here though. A lot of beautiful ladies walking around, other clubs,bars,restaurants nearby. Downtown is touristy but that pool deal is great and with the weather and ladies there, you have to try hard to have a bad time.
Society Billiards has a day special where you spend 10 bucks on food and you can play noon till 7 pm. Decent tables (with poor lighting, though) and the food is actually really good- there's a patio out front where you can watch all the girls go by and believe me you'll see enough 20 year olds in bikinis to make you cry. You can walk to the beach from there and its surrounded by bars,food,etc... Ask for Rick or Anthony if you want a friendly game here; my friends are good,not great players, and like to gamble a little bit for fun.
PM me if you want any food suggestions (fish tacos!). I left SD for work in the wine areas north and it kills me everyday. 73 degrees and mild today....sigh.