Thanks for the reply. I saw your add-on before I posted but I think, as good as it looks, it has more than what I want. My site is relatively small so I don't think the members need all of the sorting features as I don't think they would be used.
I was kind of hoping to just add the 'last seen' date and maybe the 'date registered' to the member list page. And even those additions are probably only going to be useful for me as an admin, not so much to my members.