Build a resume and interview elsewhere. Let the market determine your worth. If you get offers, then you have leverage.
Talk to your boss with leverage. Tell him that you like your job(if you do), but are under compensated. Be firm and confident. Aim high and be ready to compromise so he feels like he's made a deal. If you can't meet on level ground, then prepare to move on.
You find your value pretty easily this way. Remember that no matter how good you are, you are replaceable.
I've been down this road. Eventually I worked myself into a position where I was overpaid. That can be very tough, too. Now your options are very limited if the boss puts pressure on you. You cannot leave, you cannot under perform. I ended up leaving for two years and being rehired for $20k/yr less. I'm actually ok with it. Picked up a lot of knowlegde along the way and was able to reset expectations for my boss and myself. Now I'm just looking to get caught up with new tech before moving out on my own.