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Absolutely love my Viridian C5L. Picked it up on the EE, I know there was another one available... take a look. Ridiculous laser, great light, and great combination of settings.
Intended purpose is also a factor. If you are going to be carrying in life or death situations for part of your job or something, then you'll want to cough up the money for SureFire but you mentioned it's for a Shadow so I'll assume this is not the case.
SureFire if you can afford it, otherwise Streamlight is good value. No experience with Insight but I think it's generally regarded around on par with Streamlight.
Keep in mind that if you buy a nice Surefire, Fenix or something that isn't handgun specific you can use it anywhere. Rifle, hand-held, camping etc... I've shot in the dusk once but used my weapon light for power outages, camping etc more times than I can count in the last year.
+1 for Viridian. Can't say enough good things about it. Compact, lightweight - and unobtrusive. Plus the different combinations of light/laser settings are fantastic (on/off/strobe for each, and you can mix and match). Did I mention it's green?