How do you discover or find out about free-to-play PC games like Combat Arms, League of Legends, etc?

To coin a term, "nerd of mouth." I play League of Legends because a lot of my friends play it, and since it's free, I figured I'd give it a try. One of my friends was in the LoL beta, which he heard about through the DotA community, which I assume was the subject of outreach from Riot. Another of my friends independently learned about LoL when someone showed him some cool art from the game, because it resembled something from a tabletop RPG he plays. (Leona is totally a Solar.) In other words, gamers talk to each other about gamer stuff.

Another method is to mildly follow some smaller time gaming blogs, they tend to keep pretty well updated on these kinds of things. To name a few: http://kotaku.com/ http://www.destructoid.com/ http://www.joystiq.com/ These sites do a good job of covering most aspects of gaming and will be sure to have some stories about popular free-to-play games.

I found out about League of Legends from a site like http://www.mmofront.com/mmo/open-beta where I was accepted into beta testing. Now a few years later, I have had the pleasure of watching the evolution of League from it's conception as a "DotA remake" to a highly competitive game that propelled the MOBA industry.

I showed a buddy of mine DotA, but neither of us owned copies of WarCraft III: TFT (or lost the disks anyway) so he looked up a "free to play DotA." And that's how I learned about LoL. Combat Arms is something I found out about through the publisher (Nexon)'s ads and eventually a friend tried (and enjoyed) playing it, who then showed it to me. Generally a lot of free-to-play PC games that I've found out about are from various websites (like http://MMOHUT.com) when I looked them up from when I was bored from RuneScape (almost 7 years ago) to find something else to play. From there I found certain publishers (Perfect World, Seiya, etc etc) and kept an eye on some of their games.

Free games are free. They're not that hard to get, and they spread like wildfire. Give someone or two a great free game, and sure enough, it starts to spread. After all, who doesn't want a free game, especially if they're great? Making it free is similar to distributing a pirated version of it, making it extremely easy to distribute. You're bound to find one or two by talking to others. On the other hand we got big games like LoL, TF2 and (soon) Dota2. These guys are supported by massive companies which does the advertising for them. Dota2 made its first appearance on a 1-million prize international tournament, http://www.dota2.com/international/mainevent/results/champions/. Guess who funded that tournament? So for these games, just wander around game websites or something. There should be at least one article mentioning them. However, if you're talking about 'small' free games in development, well, your best bet is probably through developer websites. Maybe they're making it FTP, maybe looking for testers for their prototypes, who knows.

Free to plays? Or just Western games? Here in Germany you will actually find Riot Points cards in your Game stop :) In general the best games are those your friends tell you about. I started CS:S because of a friends hint, I started League of Legends because of my friends and so one. If you are into F2p check out steams and Origins F2P games, you will just see them in the shop. If you want to know about games and game announcement in general subscribe to a Games reporter or magazine on Facebook / Twitter, this way you will be informed about the newest trends and Games. I wouldn't suggest that thou, they are doing a lot of advertising and you will see yourself throwing out a lot of money for the newest games.