Firstly, I'd like to say there is a difference between "discipline" and "violence." Hitting your child because they wont listen to you is no cause for hitting them...I was spanked as a kid and so were a majority of my friends and I'm sure not listening was never the reason (directly) why they earned their spankings.
Anyway, I find the taking away of privileges pretty effective. It is for me, at least. When I was little and my mom took away my gameboy or TV time, I would have no choice but to listen to her. Sure, there was initial anger and I didn't want to listen to her at all, but once I got past that, I was the most attentive kid ever. So take away TV time (or TVs entirely if they are in their room), game systems, over-at-friend's-house time, phones, computers, etc. If possible, do it in front of them and explain WHY you are doing it. I believe that with every method of discipline parents should explain why they are doing what they are doing.
But definitely take away their "escapes" from you. Many electronics and stuff are simply escapes from what you're saying. I'm assuming your children are above the age of 2 so it will hurt a bit to have the TV and stuff taken away since most kids don't have any other ways of entertaining themselves.
