What's a good camcorder that will record video in any of iPad's supported formats?
According to Apple, the iPad is able to reproduce: 


H.264 video up to 720p, 30 frames per second, Main Profile level 3.1 with AAC-LC audio up to 160 Kbps, 48kHz, stereo audio in .m4v, .mp4, and .mov file formats; 
MPEG-4 video, up to 2.5 Mbps, 640 by 480 pixels, 30 frames per second, Simple Profile with AAC-LC audio up to 160 Kbps, 48kHz, stereo audio in .m4v, .mp4, and .mov file formats


This leads to the file formats that Flip cameras use:


  Video Format   H.264 video compression,
  AAC audio compression, MP4 files
  format


So with that in mind, I assume that Flip does it. 

However if you’re looking for a more “camcorder” thing (which you don’t specify in your question), the Sanyo’s Waterproof Xacti Camcorder does record in “Apple Friendly” format. Other than those, Google is your friend, look for “Apple friendly” camcorders. There are others out there. 

I’ve personally tried the Flip and it’s fantastic, but I don’t have an iPad. 

A word of caution: the ipad is not submersible ;)