If you're planning to visit Vancouver and want to do some preliminary research, travel forums are generally a good starting point. My reasons?
a) Travel forums offer a variety of different perspectives.
b) They offer less bias than official tourism sites.
c) They provide you with an opportunity to participate in the discourse: you can ask specific questions relevant to your situation. Likewise, you can choose to respond to questions written by others.
In no real order, here are the travel forums that I find credible and relevant to Vancouver:
Lonely Planet's Thorn Tree Travel Forum - Canada branch
Just like their books, Lonely Planet's forums tend to cater to the more alternative, budget-oriented travellers. It's a great forum to consult if you're planning to visit Vancouver on a working holiday visa, you want some advice on hostels, on public transit options, the cool off-the-beaten-path sites, and so on.
Fodor's Travel Talk - Canada forum
Fodor's tends to attract a more mature crowd which has a bit more money to throw around. If you're looking for itinerary ideas, hotel ideas, home exchange suggestions, resort information, and general information on spending time in Vancouver, there's a lot of great info here.
TripAdvisor Vancouver Forums
TripAdvisor British Columbia Forums
TripAdvisor Canada Forums
TripAdvisor is one of my favourite travel forums in existence today. It tends to attract a very diverse audience, many of whom are frequent posters, so there's always a lot of relevant info being posted daily. What makes this forum particularly helpful is that it's broken down geographically by province and city, so you can really focus on Vancouver-specific posts. While it's a useful site for obtaining travel info (like hotels, activities, itineraries, restaurants, etc.), they are very strict if you post about non-travel topics, so if you're hoping to find info or ask questions about immigration, finding a job in Vancouver, or living in Vancouver as a resident, it's not recommended.
City Data - Canada forum
This forum tends to be more amusing than useful in my experience. City Data is geared towards people wanting to gain information about American cities. City Data's forum's are therefore used almost entirely by Americans and it's virtually unknown to Canadians. While they do have a general Canada forum, it almost feels like an afterthought. The Canada forum's rather quiet and, not surprisingly, tends to feature its fair share of Canada vs. the USA comparison questions. However, every now and then you'll find some relevant gems.
Frommer's Community - British Columbia Forum
I'll give them brownie points for having broken down the Canada forum geographically into separate provinces, however, there is such little activity on Frommer's British Columbia forum (as of right now, the most recent posting is dated 12 days ago) I rarely ever use it.
VirtualTourist - Vancouver Travel Forum
VirtualTourist - British Columbia Travel Forum
VirtualTourist - Canada Travel Forum
VirtualTourist is a great site for seeking unbiased travel information, but its travel forums are definitely not its strength. VirtualTourist's Canada, British Columbia, and Vancouver forums are not frequently used, and responses will not bring the topic back up to the top, so many postings simply get lost in the shuffle. However, there are few limits to the topics one can post about, and those who take the time to ask good questions are often rewarded with thoughtful responses.
BritishExpats - Canada Discussion Forum
Despite the fact that I'm not British, I find this forum completely fascinating in an anthropological kind of way. The forum is for people who are planning to live and work in Canada. While you have to search around a bit to find the Vancouver-related topics, there's a lot of great information and first-hand advice on immigration, finding jobs, finding homes, finding a support network, understanding the local culture, etc. Although it (understandably) offers an overwhelmingly British perspective on life in Canada, you don't have to be British to participate in the forum.
SkyscraperPage Forum - Local Vancouver
SkyscraperPage - My City Photos N-Z
SkyscraperPage is not so much a travel forum than it is an online community nurtured by architecture and urban geography geeks. However, for those looking to move to Vancouver, its Local Vancouver forum offers detailed insight about all aspects of life in Vancouver. But what overshadows SkyscraperPage's city forums, in my opinion, are its photo forums. My City Photos is a forum devoted to photodocumentaries of cityscapes. If you want to get a better sense of Vancouver visually, this forum often features people's photo submissions of Vancouver's different neighburhoods. Interesting discussions can often result from the photos, especially when they feature the not-so-squeaky-clean aspects of Vancouver.
Chowhound - Western Canada forum
This is my favourite forum if you're seeking specific restaurant recommendations. Chowhound is essentially a forum for foodies. While you can get some excellent restaurant recommendations on other travel forums, Chowhound takes the cake for the food-obsessed.
Livejournal Vancouver Community
This is Vancouver's great hidden forum which is heavily used by Vancouver-based Livejournal account holders. While it's typically frequented by university students, you get all kinds of perspectives (especially from many subcultures) about all aspects of Vancouver life. This is a great forum if you're seeking specific recommendations, whether it be about schools, neighbourhoods to live in, special events, shopping, or even where you can purchase a random product that no other store seems to carry. Chances are somebody on the Livejournal Vancouver Community will have an answer.