Can you recommend a good, lightweight game (preferably with an online mode) that I can play on a Linux netbook?

My desktop rig is in a box on its way to Japan. I’ll be without a desktop for a significant amount of time (a month, more likely two).

I need a lightweight, fun game for Linux (Ubuntu Netbook Edition) that will run on a light machine such as I have:

Customised Acer Aspire One A110-L
1.6GHz Intel Atom n250
1GB DDR2–800 (single channel)
32GB SSD (~40MBps throughput, but I don’t think this will be a particular issue given the rest of the specs)

I have a mouse, obviously.

Please don’t recommend flash games; flash support in Linux is appalling, and while I can just about watch flash movies, flash games are slow to load and don’t work properly much of the time.

I like FPS, but I’m also open to 2d shooters of any stripe.

Thanks in advance for your recommendations!