Some useful sites for you
http://www.jolt.co.uk/ - huge gaming community that caters for pretty much every game
www.clanbase.com - another community site but for clans/guilds that play against each other. Clanbase is used to organise matches and holds ladders for them all. There are some amazing gamers on this site.
I used to play a lot of computer games a few years back. One in particular at that time was hugey popular which is a game called Counter Strike which still now 6 years on has a strong following.
There was a time back in that game when every team (usually involved 5 people playing together as either terrorists or counter terrorists against the another team) wanted to be rated highly in Clanbase. As time went on this site for one reason or another became uncool amongst the serious gamers. Why? Im not sure tbh, I suspect it was due to the rise in people cheating in clan base competitions.
The Jolt website Graham mentions is as he says, HUGE and I believe even years ago when I was in the scene the biggest gaming site in Europe. They just seemed to buy/absorb every major gaming forum there was. As a result of this it became so big that the community which had built up didnt feel as specialist any more and this also became a very uncool site amongst the serious gamers.
I was heavily involved in Jolt for a long time and was an admin for the game Counter Strike (basicly meant spotting and banning cheats from their public servers)
My point? No idea lol. I guess that if you are after a resource/site for finding out what current gamers consider to be cool then I would imagine the two above may not be the place to ask. The gaming communities are a very fickle bunch and moods/trends change frequently.
There is no doubt that this is a huge market, just look at Korea for whom gaming is considered a very popular spectator sport and many games have profesional players who make a good living from gaming and treat training/playing as a job. I assume that this trend will continue to expand to other countries as time goes on.
One site which used to be considered cool amongst CS players was
http://www.ukcounterterrorist.com/ which a friend from one of my teams set up years ago as an April Fools joke once to take the micky out of an existing site. This was about 4 years ago and now the original site which was once considered cool is now totally dead and the new site appears to still be thriving.
World Of Warcraft (WoW) as others have said is played by over 9 million people world wide. I used to play this at a high level but the dedication and time needed became too much. 4-6 hours 5-7 days per week minumum was too much for me as the main "tank" in a top end guild they basicly could not do anything with out me because of the mechanics of the game.
People in WoW seem to be on the whole a nice bunch of people who are helpful to random strangers they encounter in their virtual world and their age being older than those who play CS means that as a possible market they would make more sense to target. just google world of warcraft to find the home site which most players use the forum for.
For a "cool" WoW site google for "world of raids" as this used to be a good resource when I played.
In my old wow guild which had around 60 members there was a lot of them who had dabbled in one form or another in poker. if you could somehow link the two I would see it as a viable venture if you could work out a way to target the right people.
I also used to attend a "LAN party" which is basicly 1000+ geeks taking over the conference centre at Newbury race course every few months to play various games.
One of the things many people used to look forward to the most was the informal poker competitions each night. These used to attract upto 40 people I recall at one event years ago.
There is a definate relationship between gamers and online poker players.... finding it and exploiting/using it would not be easy though.
Best of luck, hope this vague info helps.
edit: damn my spelling and punctuation shows I used to play CS!
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