+1 on Framesaver. It protects the inside of the frame. It's kind of messy to work with but that's what I used on my steel Bianchi. To do a good job you need to pull pretty much everything off the frame so it's not a real quick procedure.

Other than that I just wax it really good and replaced as many of the steel screws with stainless steel ones as I could. The rest I put a thin coating of oil on. I also use stainless steel cables.