You can pretty much take your pick of any camera with a removable memory card these days, without having to have any special software besides the USB stack- if it's not supported directly as a generic mass storage device then all you need to do is get a card reader that works with Poseidon (Lexar for example).
Then it's just a matter of dragging and dropping the images off the automounted drive- almost all of them are using the FAT16 filesystem.
Now if you want to use it as a realtime webcam like some of them are capable of, that's a different story.
