There are other agents known to inhibit the hyperphosphorylation...

There are other agents known to inhibit the hyperphosphorylation of tau via glycogen synthetase kinase inhibition, resulting in stabilisation of microtubules,
lithium being one.

I'd refer readers to:

Glycogen synthase kinase-3 (GSK-3) inhibitors for the treatment of Alzheimer's disease.
Medina M, Avila J.
Curr Pharm Des. 2010;16(25):2790-8.

Lithium, a potential protective drug in Alzheimer's disease.
Engel T, Goñi-Oliver P, Gómez de Barreda E, Lucas JJ, Hernández F, Avila J.
Neurodegener Dis. 2008;5(3-4):247-9. Epub 2008 Mar 6. Review.

Activation of Wnt signaling by lithium and rosiglitazone reduced spatial memory impairment and neurodegeneration in brains of an APPswe/PSEN1DeltaE9 mouse model of Alzheimer's disease.
Toledo EM, Inestrosa NC.
Mol Psychiatry. 2010 Mar;15(3):272-85, 228. Epub 2009 Jul 21.


Trials, however, seem to have been unsuccessful thus far:

Lithium trial in Alzheimer's disease: a randomized, single-blind, placebo-controlled, multicenter 10-week study.
Hampel H, Ewers M, Bürger K, Annas P, Mörtberg A, Bogstedt A, Frölich L, Schröder J, Schönknecht P, Riepe MW, Kraft I, Gasser T, Leyhe T, Möller HJ, Kurz A, Basun H.
J Clin Psychiatry. 2009 Jun;70(6):922-31.


Another small Melbourne-based pharma, Velacor Therapeutics, is examining the use of selenium as a GSK inhibitor in a trial that is currently in progress:

http://www.melbourneventures.com/technologies/tech_Velacor.html