This is a difficult question to answer as most people are looking into this as I write this - myself included. I have never explored HSP 90, so I cannot address that one. I have however used GAPDH and B-ACTIN. I have not had much luck with B-ACTIN, but GAPDH seems to be a viable candidate over a period of a few months. One thing that I have done, which seems to help is design multiple primers so that the amplicons are of different lengths. So I have multiple GAPDH primers which results in multiple amplicons of varying lengths. So it is not just the choice of the gene, but the size of the amplicon as well.

I have also looked at 18s rRNA and 28s rRNA (same markers typically used for RNA integrity number), with varying success, depending on tissue tested and interval explored.

Hope this helps