The Armstrong pullup program which was 5 days a week and that got me to 15 deadhangs at ~185 pounds.
I've also tried the Density Training method by Ethan Reeves and it was twice a week but I can't remember how well I did.
I'm not sure what method this is considered but Robb wrote about it in one of his PM articles where he had someone doing 3-5 sets of 1-3 reps of weighted dips and pullups 3-5 times per week. That actually did a lot of good for me after I had not been doing pullups for months.
Recently after what seems like an endless line of arm injuries I've been able to dedicate training time back to the pullup without any pain and I've been able to hit a solid 13 chest to bar pullups at a weight of 189. Recently T-nation had a article about pullups and I just took the tip from Poliquin in there on doing ten sets of half my max pullups once a week. So I was doing ten sets of 4 and then a few days later I did a few max sets. Less than 4 weeks later I went from 8 pullups to 13. Now I'm back to the weighted pullups.
"And for crying out loud. Don't go into the pain cave. I can't stress this enough. Your Totem Animal won't be in there to help you. You'll be on your own. The Pain Cave is for cowards.
Pain is your companion, don't go hide from it."