Is there a good reference for the structure of the Chow ring of $\mathcal{A}_g$, the moduli space of complex principally polarized abelian varieties? More generally, references for the intersection theory, enumerative geometry, and vector bundles on $\mathcal{A}_g$ would be nice.

$\begingroup$ i would think faltings and chai would be a good place to start... i guess you've already looked at that and not found what you want? $\endgroup$ – Max Flander Mar 27 '10 at 6:09

$\begingroup$ Isn't the point of FC getting everything (and in particular the theory of compactifications of A_g) to work over Z? I think the questioner is more interested in questions over C; FC might be a bit daunting with their 14tuples of degeneration data... $\endgroup$ – Kevin Buzzard Mar 27 '10 at 7:27

1$\begingroup$ Yes, I'm interested in things over $\mathbb{C}$, so FaltingsChai is a bit terrifying to me. $\endgroup$ – Charles Siegel Mar 27 '10 at 13:33
Van der Geer has written a paper computing what he calls the tautological subring of the chow ring of $\mathcal{A}_g$. He also computes the tautological ring for a smooth toroidal compactification.
G. van der Geer, Cycles on the Moduli Space of Abelian Varieties, in "Moduli of Curves and Abelian Varieties (The Dutch Intercity Seminar on Moduli)", p. 6589 (Carel Faber and Eduard Looijenga, editors), Aspects of Mathematics, Vieweg, Wiesbaden 1999.
It is available on the van der Geer's website here
Regarding intersection theory, Erdenberger, Grushevsky, and Hulek have been working on this for the toroidal compactifications, mostly for small values of $g$. For example, see the following references.
C. Erdenberger, S. Grushevsky, K. Hulek, Intersection theory of toroidal compactifications of $\mathcal{A}_4$. Bull. London Math. Soc. 38 (2006), no. 3, 396400.
C. Erdenberger, S. Grushevsky, K. Hulek, Some intersection numbers of divisors on toroidal compactifications of $\mathcal{A}_g$. J. Algebraic Geom. 19 (2010), no. 1, 99132.
S. Grushevsky, Geometry of $\mathcal{A}_g$ and its compactifications. Algebraic geometrySeattle 2005. Part 1, 193234, Proc. Sympos. Pure Math., 80, Part 1, Amer. Math. Soc., Providence, RI, 2009.