Not listed in the order I first rode them, either, but as I thought of them. Some of them are only just barely.
The only ones of the systems listed here that I've rode completely -- that is, every bit of line open to the public -- are Atlanta (unless there's been a new extension lately that I've not noticed) and Glasgow (both loops, inner and outer). I haven't been all the way out to the end of the Pittsburgh/Bay Point line of BART, you see, or I could count that as well.
Edit, 14 Aug 12:00: And here are the logos of some fixed-guideway transit systems that don't show up on the "Metros" site but which I have ridden: