4. Seven Of Nine
It would be interesting to see what becomes of Seven of Nine when she has spent more time as Annika Hansen than she did as a Borg. As for Jeri Ryan herself, she was recently cast in Ronald D. Moore's Helix. So she's still interested in appearing in science fiction. Jeri Ryan is a fine actress. As Seven she was deliberately wooden at times, and the character didn't really get an expressly long time in which to grow, which is unfortunate as the character filled the Data/Spock brief for the later years of Voyager. Also she was set up randomly with Chakotay at the end of the series, which just seemed baffling at the time so a legitimate romantic interest for her would be interesting. Perhaps she could be involved with our number three choice...