You may know from my previous articles (like this one) that I like the Recon Ron Pullup program, mainly for two reasons:
1) It is simple to follow – you just read and do.
2) It is realistic in that the first set in a workout has the most pull-ups and the number decreases as you do the subsequent sets.
The program can be found here as a web page [Jan 2019 Edit. Page seems no longer available]. I recreated it here for those who may want it in a vertical format (with the weeks coming one below the other, rather than across). There is also a copy similar to the original one here.
I also extended the program by a few weeks.
For the sake of clarity, here are the links again. (Links will open in new window).