Even the best violet diode we have right now (around 1 watt) is hard to see the beam in a dark room. Even more so if you happen to be one of the people who's eyes don't pick up on the 405nm wavelength very well.
Most any green diode you get you'll be able to see a beam in a dark room.
Check out DTR's sale page on here to get a good idea of some commonly accessible diodes available.
Thanks for the help on the diodes I think I'll stick with green then.