Doom of Malan'tai - used some plastic parts from Trygon kit and a little bit of green stuff.
Spore - used a "Dragon Universe" toy and some green stuff.
Trygon Prime - nothing special....
My dipping method is detailed in this article
http://www.dakkadakka.com/wiki/en/Dipping_Tyranids.
Thanks for comments! The dip was messed up on the spore, you can see the run-lines because I used too much. A little dip goes a long way on models with flat surfaces.
Mez