How to invite yourself to present at another university?
One thing that sometimes works is the following: 


  Hi, I'm so and so, working with Prof. X on topic Y (my webpage). I was
  going to be in the area during (vague period) and was wondering if I
  might stop by to chat with your group about your fascinating work in
  Y'.


While this is a little passive-aggressive, I've found that more often than not, they'll ask you to give a talk, and even if not, you might get a chance to meet with the lab folks, which is the real purpose in any case. Make sure that the PI is around though.