If you are just getting started or need information or advice on flashlights, there are some great online communities that can help you out. Or at least help you spend a lot of your money on flashlights.
CandlePowerForums or just "CPF" is the biggest and most active discussion area on the internet for flashlights. They feature forums, some very good reviews, and more information than you will ever be able to read. They also have CPFMarketplace where flashlight dealers and manufacturers post information and private parties can buy and sell flashlights and accessories.
Budget Light Forums or just "BLF" is another online community that specializes in discussion of budget lights, but also has active discussions about flashlight modding and user experiences at many different budget dealers.
r/flashlight a pretty active forum on Reddit
Flashlight News Forums no longer active, a smaller online group, but there is some good stuff here.
The Bright Side no longer active, branched off a Malaysian general discussion area to focus on flashlights. Hosted by Lumens Review.
Flashlight Forums no longer active, another smaller forum
EDC Forums dedicated to all kind of things people might carry every day like guns, knives, flashlights, etc. There is some good flashlight stuff in their flashlight subforum.
Fonarevka Forums Russian project: all about flashlights and other lighting technology. Flashlights tests and reviews, Power supplies and chargers, Custom Flashlight Builders and Modders and etc.