I'm devoting some blog-space to the above topic, and though I think I have a pretty complete knowledge of characters in the mainstream up to the late 1990s, I don't know whether or not there have been any major characters in any comics-genre since that period.
I have the general impression that GEN 13's Rainmaker is one of the few characters to have enjoyed a regular venue on into the 2000s and/or 2010s. Other than her, no one comes to mind, though I think Red Wolf is due to get a revival. BTW, I'm not just talking heroes, but villains and support-characters as well.
If anyone cares to weigh on on the most significant N.A. characters, that's OK too. I seem to remember a thread of that nature on the old boards.