Reference for ring structure on Thom spectra I have been asked to provide at reference for the fact that if $X\to B(BG)$ (where $G$ is the stable auto-homotopy-uquivalences of spheres - or $BG=Pic(S)$ in some peoples terminology) then the Thom spectrum associated to the based loop map
$$ \Omega X \to BG=Pic(S) $$
is a ring-spectrum. I was looking around for a good reference, but couldn't find one that was very clean cut (the paper is about something in symplectic geometry - so I would like the reference to be precise). I also don't know where this originally appeared - so I would prefer the original reference if it is clear or a reference that points back to the original.
 A: The late Gaunce Lewis's 1978 PhD thesis ``The stable category and generalized Thom spectra'' proved (as a special case) that the Thom spectra of $F$ and its oriented version $SF$ (alias $GL_1(S)$ or $SL_1(S)$) are $E_{\infty}$ ring spectra, the most highly structured kind of ring spectrum.  The published version is Chapter IX of Springer LNS 1213, http://www.math.uchicago.edu/~may/BOOKS/equi.pdf, which was written so as to be as independent as possible of the previous chapters. 
A: Along the great references cited above, I think
Mahowald, Mark; Ray, Nigel
A note on the Thom isomorphism. (English) Zbl 0469.55007
Proc. Am. Math. Soc. 82, 307-308 (1981).
is also a good reference. Theorem 1 of this paper, proved as Corollary 3, is what you are after. I must add that Theorem 1 of this paper was originally proved in "Mahowald. Ring spectra that are Thom complexes" that is cited above.
I also like to add that Thom spectrum of a map from a loop space into $BG$ is not necessarily a ring spectrum! The statement is that the Thom spectrum of any $H$-map, in particular loop map, is a ring spectrum. 
A: I think that the original paper is

Mahowald - Ring spectra that are Thom complexes

My favorite reference for the multiplicative properties of Thom spectra is

Antolín-Camarena, Barthel - A simple universal property of Thom ring spectra

