Nessa is very pretty. I also like Nessie, as in the pet name for the Loch Ness monster. :-) Well, I see the usual suspects have already been suggested (
Vanessa,
Agnes,
Nerissa).
Creative, eh? Well, any noun ending in "-ness" would work. Happiness is the only one I can think of off the top of my head, but there must be scores more. Other ideas:
Innisfree ("IN-ish-free")(If you're a
William Butler Yeats fan)
PrudenceHortensiaClemenceNan ESther (N + Es)
JessamineGlynisNerys
OK, so some of these are reeeeaaaally stretching it. but happy hunting and be sure to let us know if you settle on something. Thanks for a fun challenge.