I invested in a 75lb weight vest and that thing kicks my arse. I can only do about 4 pull ups with the 75lbs, and 7-8 with the 50lbs. I can really fly through them without it on though. Best I ever did was 39 pull ups. Couldn't get the 40 for the life of me. If we are talking strict dead hangs, I can get around 20.
I disagree with the "don't kip" mentality. Kipping is like one handing a saw, its worth learning to do safely. You should do strict pull ups most of the time, but kipping teaches your body to do the most work with the least effort. (Think just pulling yourself up ddrt without humping the air).
A workout I use to do with some friends who were as nuts as I am is called murph. You run a mile, then do 100 pull ups, 200 push ups, and 300 jump squats. You finish it off by running another mile. Then you lay in bed for a couple days straight and ponder life.
Seriously though, a weight vest will really help out. Make sure you warm up before doing anything weighted (and don't static stretch before weight lifting, it increases likelihood of injury). I pulled a muscle in my back the first time I tried weighted pull ups without warming up, not fun.