Towel Pull ups:
It's pretty simple. Take the towels, loop them over the bars and grab the damn things and do some pull ups. This is a good way to train your grip, and though I am no Adam, I get the feeling everyone can benefit from grip training.
Rolling Thunder/Vertical Bar Pull ups
tests best for you.
Crush Pull Up:
The options are limited by your imagination, and this is not a complete list. The important thing is to test your variation, and find which is best. The more often you can do a pullup, the better you will get at them.