The best way I know to id them is to post a pic for Bob or Appy on the bluecrayfish board. They can id faster than fast!
Other than that, try this.
Are they wild caught or store bought? (Location if wild caught can narrow down species)
How long/large are they and how long have you had them? (Most North American species get no bigger than 6 or 7 inches)
Do they have narrow heads and rostrums and prominent eyestalks? (This is usually indicative of Australian species)
Check out Crayfishworld.com He has tons of pics of different species posted.
I'd like to keep the thread going too!