Game servers allows gamers more control over their online gaming experience than they would find in a MMORPG or even an Online RPG. With a game server, you can host the game you want and only allow the people you want to play. Besides hosting LAN parties or guild battles, a game server can also be used to host your own online game. Below is a list a of game server resources, game server browsers, and even game networks. 

Battle.net
One of the first and most known game networks with such all-time classics as Starcraft, the Diablo franchise, and the Warcraft franchise.

Little Golem
Game server/network that lets you play turn-based board games on the Internet.  

Antiworld
NWN PvP server. The aim of the game is to capture the enemy team's flag and return it to your team base, gaining experience and points for your team every time you do so successfully. Be careful though, Retrieving the flag isn't easy, when you hold it you suffer reductions in power, speed, hide skill and ability. You are in a team for a reason - use your team mates! One of the things that can spoil NWN team PvP servers is being constantly killed by higher level characters than you, it can really spoil your fun. In Antiworld CTF there is a system so people cannot attack characters outside their level range, and if they do punishments are instantaneous and painful.

Kali.net
Popular game server browser service that has been around for years. 

aGSM
Free game server utility that shows you both Local Area Network and Internet game server info so you can easily find which games to join.  

Hosting A Game Server
Excellent article that informs you on how to run your own server for online gaming.  

Firewall Help
Article the helps you operate a game server through a firewall.

QStat
QStat is a command-line program that gathers real-time statistics from Internet game servers.

Steam
The game service that powers Half-Life 2.

Yahoo Game Server Browser
Allows you to find online game servers for games you are interested in such as Counter-Strike and Battlefield 1942.