If you're interested in arcade space shooters (think Rafkill, Raiden, or something similiar), take a look at Irukandji .
It's recently ported to Linux, and has a pay-what-you-want option- $1 or more gets you all 3 platforms to download.
In addition, there is also a demo.
It plays rather differently depending on your graphics card- on my Intel 945, it plays like you are swimming in the ocean- everything moves slower, and there's a certain sluggishness to it. It's still quite playable and enjoyable.
With the Windows PC I have with a Radeon 200 Xpress, it plays smoothly and you move around the screen without any sluggish feeling.
The guy is planning to bring over all his games to Linux.