5x5 bb curls (if you're not going heavy enough this should fix it)
2x8 incline DB (stretch exercises increase IGF receptors apparently)
2x8 preacher curls (for the brachialis to push out your bicep)
One common problem with people being disatisfied with their workout is form...is your form correct (I know its a simple exercise but I still see people screwing up on their form).
Soreness is not a good indicator of exercise session effectiveness. Your nervous system starts to adapt to it. My bicep was sore the first time I curled and I couldn't move my arms for a week (I couldn't extend them and daily chores became hell). Now I can curl 3x the amount and I feel absolutely nothing.
Squats should definately grow your biceps via endocrine system

. A 5x5 at 85% (hence the 5 reps) should get enough testosterone floating around.
Preacher/concentration curls aren't really for mass, BB curl = most basic and most effective for mass building.
Serea, do reverse curls to workout your brachialis it could be a potential achilles heel

. A weak wrist can jeopardize bicep potential (if your wrists gives before your biceps while doing a bicep targetted exercise).
Rows/Pullups should hit your bicep to some degree too, or at least grow them via anabolic hormone release.