[Espy]

And there are also body mods like tails and stuff.

Transparent skins that I can remember right now:

Full:
Solukino
Jellyfisher
Knox of the Night -- I'm actually not sure if this one's transparent. It looks nice, though.

Partial -- these are more like tattoos, but less known and less line-y than, say Cyber Reaper or Spirit of the Tribe:
Knox of the Night
Petal Dancer
Zephyr's Companion

To be honest, transparent /clothing/ items often work just as well.