Is this the original Unreal? If so, I'd suggest Unreal Tournament or Quake III for first-person shooters. Both have enough mods out there to make them fun for a long time. One of my most favorite games to play on a network, though, is Myth II. It's a great real-time strategy game. Plus, I believe the Myth Total Codex (which has Myth, Myth II, and a ton of maps) is only $20. There's just something about dwarves with moltav cocktails...