Nobody is close to OSU in overall consistency. I don't know who might be second.
USC.
USC is second but Ohio State is so far ahead that #2 USC is about as close to #9 Alabama as they are to #1 Ohio State.
i might go oklahoma. particularly if we're talking consistency within the ap poll (are we? not sure why i was thinking that).
can't seem to find it now, but ou seemed to edge out bama, mich, nd and usc as the fairly clear second most consistently highly ranked team. bama had the #1, but ou was just behind. osu and ou were almost tied for top 5 consistency, osu dominated the top 10, with ou distant second. same with top 25 overall, but mich and nd came into play. i'm sure usc was in the mix for those as well, just can't remember and can't find the data on quick search.
could probably make a case for all the blue bloods, really. some have few down periods and longer dominance, but down periods last a little longer (mich, nd). some have more down periods, but bounce back quicker (bama, ou). not sure where usc falls in those.
and then there's osu, that just doesn't have a down period. not like the rest of us. don't hit the heights, at least not quite as often, but they're always right there.