This is the link if you want to try it yourself:
Cross Processing in Photoshop - color negative art effect | PhotoshopSupport.com
These are my images:
Blue cross process
Brown cross process
Green and brown cross process (my favourite)
If you have an iPhone4 there are a bunch of apps which help this process and save time.
RetroCamera and Mill Colour are pretty good. PictureShow is loads of fun and does all sorts of other natty things, the image below was made with it.
My favourite app is Hipstamatic, which has lots of lenses, films and flashes to use and experiment with.