Michael's involvement in the whole Psi-Corps thing is a possibility as well. There is a Psi-Corps trilogy as well, though the third book is probably my favorite - Bester's a fugitive, Michael's using every resource he has to find him, and it just goes on.

*grins* I suppose it's pretty easy to forget about David. He was never seen, just mentioned in the final few episodes, as well as in the time-travel episode when the future Delenn told Sheridan that their son was safe. There are further mentions of him in some of the books, and he even plays a part in a few of them - the novelization of In the Beginning, the Centauri trilogy, maybe one or two others. I can't quite recall any others at the moment.