Alien Arena 2007, which is a part of our free multiplayer games list has been reviewed by Linux.com.  Nexuiz, Alien Arena 2007, and Open Arena are the best open-source first-person shooters that you can download as far as I'm concerned.  Linux.com also adds Tremulous, which steps outside of the traditional FPS to me.  Version 6.10 was just released and here are some of the changes:

How does 7 brand new, gorgeous arenas to play in sound?  How about a more balanced and responsive weapon set?  Do you like to 1v1?  Well we now have a duel mode!  The gameplay of Alien Arena was the big focus this release, and you'll see the difference immediately.  Weapons now respawn in five seconds rather than twenty.  A Q3 style health and ammo system has been implemented, to help prevent weapon camping, as well as a random spawning quad.  Last but not least, version 6.10 presents a brand new weapon, the Violator!

Check out the Alien Arena 2007 official site.  Give it some time, it is being slashdotted today. 

2Moons, a free MMORPG that focuses on PvP, is holding several events for the month of October collectively called the Blood Moons events.   Here's some of the events that will be available starting October 12th.

• GM PK event -- Duel a GM or VGM and if you win, you get prizes.
• GM Hide and Seek -- Find a GM during this event and get a prize.
• Trick or Treat -- Mobs will drop candy that will temporarily boost stats.
• Collection Challenge -- Collect the above candies instead of using them and whoever gets the most, gets a prize.
• Night of Horrors -- For this one day, GM's will spawn different level creatures at random places in the world. 

Check it out over the official 2Moons site.

It looks like th Unreal Tournament 3 demo might be released on FilePlanet today.  Basically, it is available for pre-load to FilePlanet members, and the public can try to get into some reserve spots.  I just got into a spot with no problem, but you must have FilePlanet's download manager up and running, because that application will start the download when it becomes available.  You can also use Gamespy Comrade (a small application that runs on your desktop like XFire) to notify you when the download becomes available.   Find all of this and other details at the Fileplanet UT3 promotional site.  This game has been a long time in the making, and was supposed to be released in the spring earlier this year.  I'm anxious to see where they have took Unreal Tournament 2004, which was a great multiplayer game. 

UPDATE:  Destructoid reports that you may be able to get this demo early using this link (click the blue box, it's a site in Norway).  The queue looks long though, I'm number 791 in line. 

UPDATE 2:  Just got an email that Fileplanet's demo will be available at 3 PM ET. 

ExtremeTech has a graphics card upgrade guide up in response to all the great PC games that have been released and are going to be released this fall.  If your looking to upgrade soon, you might want to read through this guide.  I just upgraded to a EVGA GeForce 8600GT this week, and I must say that I am impressed with the performance you can get out of a card you can get around $100.  I got mine for $110 and it had no problems running the Call of Duty 4 demo at 1280x1024 with 4x antialiasing turned on. 

In addition, you should also check out the Tom's Hardware article, best gaming graphics cards for the money in October.  With high-definition games like Crysis, Unreal Tournament 3, and Assassin's Creed coming out soon, and with graphics cards taking a price cut recently, it's a great time to upgrade.  The Extreme Tech guide does mention a new nVidia card rumored to come out around November that will be in the $200 range.  You may want to wait around to as close to Christmas as possible before finally deciding on a card if that's your price range. 

The previously promised Call of Duty 4 demo has been put up over at Yahoo Games, check it out:  At a cool 1.4GB, this game must have some awesome graphics.

Min specs aren't too bad either:

CPU: Intel(R) Pentium(R) 4 2.4 GHz or AMD(R) Athlon(TM) 64 2800+ processor or any 1.8Ghz Dual Core Processor or better supported
RAM: 512MB RAM (768MB for Windows Vista)
Hard Drive: 8GB of free space
Video card: NVIDIA(R) Geforce(TM) 6600 or better or ATI(R) Radeon(R) 9800 Pro or better

http://videogames.yahoo.com/events/call-of-duty-4/call-of-duty-4-demo/533701

Update:  Had some problems with the Yahoo download, so here's the Filefront link also:

http://files.filefront.com/Call+of+Duty+4+Modern+Warfare+Demo/;8774322;/fileinfo.html