Catching up on some recent sightings:
6UCK846, or GUCKBAG. I don't know what a guckbag is, but it doesn't sound pleasant.
7ARG376, OR TARGET6. I just thought that this one was cool because the first six characters made a whole word. Too bad it didn't end in a 5.
5LLY900 (zero-zero), either SLLYGOO or SLLYPOO. Silly poo or silly goo
5WAY717, or SWAYTIT. Usually they sway in pairs, but one is cool, too. I say, long may it sway!