Honestly? One of my gotos is
youtube
i find it very helpful to see what other people are doing in places. Granted, there are a lot of terrible videos, but I spent a lot of time watching before I went to Thailand. Gave me some ideas of where I might want to go, and what I should expect once there
I also do spend a lot of time on
tripadvisor . I find this more useful for urban and all-inclusive style vacations. It's interesting to see what people think of a resort, although I would recommend taking the top and bottom reviews and assuming the truth lies somewhere in the middle. Sometimes if they are complaining about food or crowds or conditions of facilities, the included pictures help explain their complaints.
I find forums are hit or miss. This is a great forum - i can ask a question, and get lots of information. I was trying to find out some information on a previous trip (i don't remember which one) and lots of people recommend a specific forum. I joined, and ran into the problem that despite all the recommendations, there was no one posting there. The information that was still there was approaching 10 years old.