Camden is awash with pubs. As has been said there are many up Parkway, which is just over the road from Camden Town tube, including the Dublin Castle, which is famed for its live music.
Dont go in the Worlds End (opposite the tube) its a rancid place with even worse beer, jsut avoid it.
Walking up Chalk Farm Road (right exit from Camden Town tube) from the tube to the Roundhouse, the first pub of worth is off to the left up Inverness Street, called the Good Mixer. Its a proper spit and sawdust bar, couple of pool tables, sky sports, not very good draught but good atmosphere and cracking Jukebox. You could call it a punk bar, but I dont like to label, and thats something thats hard to do in Camden anyway.
Next up back on the main road is the Elephants Head. Again the draught in here leaves a lot to be desired (honest, Im not THAT much of a beer snob) but I do like the atmosphere. Teddyboys, rockers, mods, punks, goths and indie kids all happy together, and a great rockabilly disco on a Saturday.
Carrying on up the road and just after the bridge, on the right hand side is Hawley Road, and 30 seconds walking down there will find you the Hawley Arms. What once was a scruffy biker bar is now a great pub. Dont believe what you read in the tabloids, it really isnt that much of a celebraty hangout, though some of the staff may sometimes think it is (most are down to earth). The foods decent, the beer grand, and a cracking jukebox. Its got a little back yard (and I meen little) and a decent roof terrace with a couple of heater lamps.
If you carry on down Hawley Road (about another 2 mins) youll come to Quinns. Although your walking perpendicualr to the Roundhouse at this point its worth it if you like your beer. You can also get here straight from the tube, turning out the left exit and heading up Kentish Town Road. Its an old family run Irish pub (though not Irish theme) with a fantastic range of ales and lagers on tap, and many many more belgian and german beers in bottles. Also does good food and has all the sport. Music is not one reason to go there, though its quiet.
Back up on Chalk Farm Road and youll come to the Loc Tavern (getting close to the Roundhouse now). A great boozer, with decent music, and beer and food. Its got a large backyard (covered to an extent) and an upstairs that also has a roof terrace. It can get very busy in here, at the weekends, and theres normally live music on a Sunday.
After the Loc theres a restaurant called Cottons, that does Caribean food, but also has a small front bar that does blinding Rum cocktails. Go easy on them though, as they are very strong!
The last pub before the Roundhouse is Bartok, a smart boozer that I rarely go in, but has a nice decor.
Thats just my list, there are many many more boozers in the area, but I'd (and often do) happily drink in all of these above.
Cheers.
Oh and the Roundhouse obviously has a bar, but you wont be in there till doors open. It also has a smoking area next to it so dont worry smokers.